Alternating etch and passivation process

ABSTRACT

Tin oxide films are used as spacers and hardmasks in semiconductor device manufacturing. In one method, tin oxide layer (e.g., spacer footing) needs to be selectively etched in a presence of an exposed silicon-containing layer, such as SiOC, SiON, SiONC, amorphous silicon, SiC, or SiN. In order to reduce damage to the silicon-containing layer the process involves passivating the silicon-containing layer towards a tin oxide etch chemistry, etching the tin oxide, and repeating passivation and etch in an alternating fashion. For example, passivation and etch can be each performed between 2-50 times. In one implementation, passivation is performed by treating the substrate with an oxygen-containing reactant, activated in a plasma, and the tin oxide etching is performed by a chlorine-based chemistry, such as using a mixture of Cl2 and BCl3.

INCORPORATION BY REFERENCE

An Application Data Sheet is filed concurrently with this specificationas part of the present application. Each application that the presentapplication claims benefit of or priority to as identified in theconcurrently filed Application Data Sheet is incorporated by referenceherein in its entirety and for all purposes.

FIELD OF THE INVENTION

This invention pertains to methods of semiconductor devicemanufacturing. Specifically, embodiments of this invention pertain tomethods of using tin oxide films in semiconductor processing.

BACKGROUND

In integrated circuit (IC) fabrication, deposition and etchingtechniques are used for forming patterns of materials, such as forforming metal lines embedded in dielectric layers. Some patterningschemes involve the use of spacers that enable precise patterning andformation of small-scale features. Spacers are formed on a substrate,such that they are separated by defined distances (typically determinedby previous patterning), and are used as masks for patterning ofunderlying layers. The materials of spacers and of surrounding layersare selected to have appropriate etch selectivity that would enable bothformation of spacers, and patterning of underlying layers. After thepatterning is completed, the spacers are removed by etching, and are notpart of the final fabricated semiconductor device.

Spacers are used for patterning in a variety of applications, includingformation of dynamic random-access memory (DRAM), patterning fins in finfield effect transistors (finFETs), and in back end of line (BEOL)processing.

The background description provided herein is for the purposes ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

SUMMARY

In one aspect, a method of processing a semiconductor substrate isprovided, where the method includes: (a) providing a semiconductorsubstrate having a plurality of protruding features over asilicon-containing layer, wherein the semiconductor substrate comprisesan exposed tin oxide and an exposed silicon-containing material of thesilicon-containing layer; (b) passivating the exposed silicon-containingmaterial towards a tin oxide etch chemistry; (c) etching the exposed tinoxide using the tin oxide etch chemistry; and (d) repeating operations(b) and (c) such that operations (b) and (c) are performed in analternating fashion. Using this method, a tin oxide footing nearprotruding features can be reduced without causing damage to thesilicon-containing layer.

In some embodiments the silicon-containing material is at least one ofamorphous silicon, silicon oxide, SiON, SiOC, SiONC, SiC, and SiN.Etching tin oxide in (c), in one embodiment includes usingchlorine-based etch chemistry and exposing the semiconductor substrateto a plasma-activated chlorine-containing reactant selected from thegroup consisting of Cl₂, BCl₃, and combinations thereof. In someimplementations, plasma is formed in a process gas that includes achlorine-containing reactant selected from the group consisting of Cl₂,BCl₃, and combinations thereof, and a diluent gas selected from thegroup consisting from helium, neon, argon, and xenon and combinationsthereof.

In one embodiment, etching tin oxide in (c) includes etching the tinoxide using a hydrogen-based etch chemistry that results in a formationof a tin hydride. For example, etching the tin oxide using ahydrogen-based etch chemistry can be performed by contacting thesemiconductor substrate with a plasma-activated hydrogen-containingreactant selected from the group consisting of H₂, HBr, NH₃, H₂O, ahydrocarbon, and combinations thereof.

In some embodiments, the passivation of the silicon-containing layer isperformed by treating the substrate with an oxygen-containing reactant.For example, silicon-containing layer may be passivated by treating thesubstrate with a plasma-activated oxygen-containing reactant. Inspecific embodiments, plasma formed in a process gas comprising a gasselected from the group consisting of O₂, O₃, SO₂, and CO₂.

In some embodiments, passivation step (b) is performed before etch step(c). In some embodiments, etch step (c) is performed before passivationstep (b). In some embodiments steps (b) and (c) are performed between2-50 times.

In some embodiments, the protruding features include horizontal surfacesand sidewalls and the method reduces a tin oxide footing at thesidewalls of the protruding features.

In one implementation, the silicon-containing material is selected fromthe group consisting of amorphous silicon, silicon oxide, SiON, SiOC,SiONC, SiC, and SiN, the passivating in (b) includes treating thesubstrate with a plasma-activated oxygen-containing reactant, andetching in (c) includes etching the tin oxide using a chlorine-basedetch chemistry that comprises exposing the semiconductor substrate to aplasma-activated chlorine-containing reactant selected from the groupconsisting of Cl₂, BCl₃, and combinations thereof.

In some embodiments passivation in (b) includes treating thesemiconductor substrate with a nitrogen-containing reactant.

In some embodiments, the method further includes: applying thephotoresist to the semiconductor substrate; exposing the photoresist tolight; patterning the photoresist and transferring the pattern to thesemiconductor substrate; and selectively removing the photoresist fromthe semiconductor substrate.

In another aspect, an apparatus for processing a semiconductor substrateis provided where, the apparatus includes: (a) a processing chamberhaving a support for the semiconductor substrate and an inlet forintroduction of one or more reactants into the processing chamber; and(b) a controller comprising program instructions for: (i) causingpassivation a silicon-containing layer on a semiconductor substratetowards a tin oxide etch chemistry; (ii) causing etching of a tin oxideon a semiconductor substrate; and (iii) causing a repeating, in analternating fashion of (i) and (ii). In some embodiments (i) includescausing treatment of the semiconductor substrate with a plasma-activatedoxygen-containing reactant (e.g., plasma-activated O₂). In someembodiments (ii) includes causing etching of the tin oxide using achlorine-based chemistry. In some embodiments (ii) includes causingetching of the tin oxide using a hydrogen-based chemistry. In someembodiments the program instructions include instructions for performing(i) and (ii) in an alternating fashion between 2-50 times.

In another aspect an apparatus is provided, where the apparatus includesa process chamber and a controller having program instructions forcausing any of the methods provided herein.

In another aspect, non-transitory computer readable medium is providedcontaining code configured for performing any of the methods describedherein.

These and other aspects of implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the description below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F show schematic cross-sectional views of a semiconductorsubstrate undergoing processing that involves spacer formation.

FIG. 2 is a process flow diagram for a method according to an embodimentprovided herein.

FIGS. 3A-3E show schematic cross-sectional views of a semiconductorsubstrate undergoing processing according to an embodiment providedherein.

FIG. 4 is a process flow diagram for a method of forming tin oxidespacers according to an embodiment provided herein.

FIGS. 5A-5C show schematic cross-sectional views of a semiconductorsubstrate undergoing processing according to an embodiment providedherein.

FIGS. 5D-5G show schematic cross-sectional views of a semiconductorsubstrate undergoing processing according to another embodiment providedherein.

FIGS. 5H-5K show schematic cross-sectional views of a semiconductorsubstrate undergoing processing according to another embodiment providedherein.

FIGS. 5L-5O show schematic cross-sectional views of a semiconductorsubstrate undergoing processing according to another embodiment providedherein.

FIG. 6 is a process flow diagram for a method of semiconductor accordingto an embodiment provided herein.

FIGS. 7A-7C show schematic cross-sectional views of a semiconductorsubstrate undergoing processing according to an embodiment providedherein.

FIG. 8 is a process flow diagram for a method according to an embodimentprovided herein.

FIGS. 9A-9C show schematic cross-sectional views of a semiconductorsubstrate undergoing processing according to an embodiment providedherein.

FIG. 10 is a process flow diagram for a method according to anembodiment provided herein.

FIG. 11 is a schematic presentation of an apparatus that is suitable foretching tin oxide using etch chemistries provided herein.

FIG. 12 shows a schematic view of a multi-station processing systemaccording to an embodiment provided herein.

FIG. 13 is a process flow diagram for a method according to anembodiment provided herein.

FIGS. 14A-14C show schematic cross-sectional views of a semiconductorsubstrate undergoing processing according to an embodiment providedherein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Methods that employ tin oxide films in semiconductor devicemanufacturing are provided. The methods utilize a number of etchingprocesses with tunable etch rates and selectivities that allowintegration of tin oxide films into process schemes that employ a widevariety of materials, such as silicon-containing compounds (e.g.,silicon oxide (SiO₂), silicon carbide (SiC), silicon nitride (SiN),silicon oxycarbide (SiOC), silicon oxynitride (SiNO), siliconoxycarbonitride (SiCNO), and silicon carbonitride (SiCN)), elementalsilicon (Si), carbon (including amorphous carbon and diamond-likecarbon), photoresist, carbon-containing compounds (e.g., organicpolymers, metal carbides, tungsten-containing carbon), metals (e.g.,tungsten), metal oxides (e.g., titanium oxide, hafnium oxide, zirconiumoxide, tantalum oxide), and metal nitrides (e.g., tantalum nitride (TaN)and titanium nitride (TiN)). In some embodiments tin oxide is etched ina presence of any of these materials with an etch selectivity of atleast about 10:1, such as at least about 20:1. In some embodiments, anyof these materials is etched in a presence of tin oxide with an etchselectivity of at least about 10:1, such as at least about 20:1.

In some embodiments, tin oxide is used in patterning processes, wherethe tin oxide film is a spacer, or a hardmask (e.g., a middle layerpositioned below photoresist and above a target layer). For example, tinoxide can be a spacer in self-aligned spacer-assisted patterning, amiddle layer in self-aligned double patterning (SADP) or self-alignedquadruple patterning (SAQP), a contact hole hard mask, an extreme UV(EUV) hardmask, a reverse tone mask, or a back end of the line (BEOL)hard mask. In conjunction with selective etching processes, tin oxidemeets stringent critical dimension (CD)/profile and selectivityrequirements that are imposed by these applications. The etchingprocesses can be implemented on a variety of tools that allow plasmaetching, such as Kiyo® and Flex™ etch tools provided by Lam ResearchCorporation.

Tin oxide can be etched selectively to a wide variety of materials usinghydrogen-based etches that convert tin oxide to volatile tin hydrideproducts (e.g., tin tetrahydride). The term “tin hydride” as used hereinincludes a plurality of tin hydrides (compounds with tin-hydrogenbonding) and is not limited only to tin tetrahydride (SnH₄)). Terms like“tin chloride” and “silicon fluoride” similarly may include multiplechlorides and fluorides. Tin tetrahydride, unlike hydrides of many othermetals, has a low boiling point, and therefore can be easily removedfrom the process chambers by purging and/or evacuation thereby makinghydrogen-based etch a particularly attractive process for selective tinoxide etching.

Tin oxide, as used herein, refers to materials that include tin (Sn) andoxygen (O), and may optionally include hydrogen. Tin oxide, as usedherein, may further include small amounts of other elements, such ascarbon, and nitrogen, where the total amount of other elements is 10atomic % or less (where hydrogen is not included in the calculation ofthe content). For example, ALD-deposited tin oxide can contain about0.5-5 atomic % carbon. Tin oxide can be deposited, for example, by ALD,PECVD, or PVD. The stoichiometry of tin oxide generally can vary. Insome embodiments the atomic ratio of tin to oxygen is about 1:2 (SnO₂).It is understood that small deviations from 1:2 tin to oxygenstoichiometry are possible in SnO₂ and are within the scope of SnO₂structure. For example, O to Sn atomic ratio is between about 2.0-2.3 insome examples of SnO₂. Tin oxides with O to Sn ratio of between about1.5-2.5 are within the scope of SnO₂ material, as used herein. Tin oxidematerials described herein are distinct from indium tin oxide materials,and other mixed oxides.

It is understood that in other chemical compounds as used herein,stoichiometry may vary, unless it is specified. For example, formulassuch as SiN and HfO specify the elements that are present but not thestoichiometry. Further, it is understood that materials described hereinmay include hydrogen (even if not specified in the formula) and smallamounts of dopants not explicitly listed in the chemical name (such asless than 10 atomic % of a dopant).

The term “semiconductor substrate” as used herein refers to a substrateat any stage of semiconductor device fabrication containing asemiconductor material anywhere within its structure. It is understoodthat the semiconductor material in the semiconductor substrate does notneed to be exposed. Semiconductor wafers having a plurality of layers ofother materials (e.g., dielectrics) covering the semiconductor material,are examples of semiconductor substrates. The following detaileddescription assumes the disclosed implementations are implemented on awafer. However, the disclosed implementations are not so limited. Thework piece may be of various shapes, sizes, and materials. In additionto semiconductor wafers, other work pieces that may take advantage ofthe disclosed implementations include various articles such as printedcircuit boards and the like.

In some embodiments, provided selective etch chemistries are used toremove certain materials or features on a substrate without removingother materials or features. As used herein, the etch chemistry“removes” a material or feature when at least 90% (such as 100%) of thematerial or feature is removed (referring to thickness in verticaldirection). The term “without removing”, as used herein means that atleast 50% of material or feature (such as at least 80%) remains afterthe etch, where % refers to thickness in a vertical direction.

In some embodiments provided methods are used to remove materials fromhorizontal surfaces without removing materials residing at sidewalls ofprotruding features. It is understood that horizontal surfaces, as usedherein, include surfaces with local deviations from horizontal plane,such as convex caps on top of protruding features.

A variety of etch chemistries have been developed for selective etchingof tin oxide in a presence of other materials, as well as for selectiveetching of other materials in a presence of tin oxide. Selective etchingof tin oxide in a presence of another material refers to tin oxideetching, wherein the ratio of the etch rate of tin oxide to the etchrate of the other material is greater than one, and wherein the othermaterial is exposed to the same etch chemistry as tin oxide at any timeof the etching process. For example, the other material may be exposedwhen the etching begins, or may become exposed during the course ofetching. Etch selectivity for selective etching of tin oxide in apresence of another material refers to a ratio of an etch rate of tinoxide to an etch rate of the other material for a given chemistry. Forexample, tin oxide can be selectively etched in a presence of asilicon-containing compound using a hydrogen-based etch chemistry withan etch selectivity of greater than 50.

Similarly, selective etching of a material in a presence of tin oxiderefers to such etching of that material, where the ratio of an etch rateof that material to the etch rate of tin oxide is greater than one, andwherein tin oxide is exposed to the same etch chemistry as the etchedmaterial at any time of the etching process. For example, tin oxide maybe exposed when the etching begins, or it may become exposed during thecourse of etching. Etch selectivity of a selective etch of a material ina presence of tin oxide refers to a ratio of an etch rate of thatmaterial to an etch rate of tin oxide for a given chemistry. Forexample, carbon can be selectively etched in a presence of tin oxideusing an oxygen-based etch chemistry with an etch selectivity of greaterthan 50.

In some embodiments a semiconductor substrate is provided, where thesemiconductor substrate includes an exposed tin oxide layer and a layerof a second material, where the second material may be exposed or notexposed. Next tin oxide is selectively etched in a presence of thesecond material using one of the selective tin oxide etch chemistriesdescribed herein. For example, tin oxide can be selectively etched usinga hydrogen-based chemistry and/or chlorine-based chemistry. The secondmaterial may be exposed prior to this etch or may become exposed duringthe course of tin oxide etching.

In some embodiments a semiconductor substrate is provided, where thesemiconductor substrate includes an exposed layer of a first materialand a layer of tin oxide, where the tin oxide may be exposed or notexposed. Next, the first material is selectively etched in a presence ofthe tin oxide using one of the selective chemistries described herein.The tin oxide may be exposed prior to this etch or may become exposedduring the course of tin oxide etching.

Hydrogen-based etch. In some embodiments selective tin oxide etching isperformed using a hydrogen-based etch. Hydrogen-based etch involvesexposing tin oxide to a hydrogen-containing reactant (typically withplasma activation of the reactant) such that it converts tin oxide to avolatile tin hydride. SnH₄ has a boiling temperature of −52° C. and canbe easily removed from the process chamber. Examples ofhydrogen-containing reactants include H₂, HBr, NH₃, H₂O, andhydrocarbons (such as CH₄). Mixtures of hydrogen-containing reactantscan also be used. Hydrogen-based etching involves forming a plasma in aprocess gas containing a hydrogen-containing reactant, and, optionally,an inert gas, and contacting the substrate with the formed plasma.Examples of inert gases include nitrogen (N₂), helium (He), argon (Ar),and neon (Ne), and xenon (Xe). In some embodiments H₂ is the preferredhydrogen-containing reactant, and in some embodiments it is preferableto form plasma in a gas that contains at least 50%, such as at least 80%H₂ by volume. In other embodiments HBr is used as thehydrogen-containing reactant. For example, tin oxide can be selectivelyetched with a plasma formed in a process gas consisting essentially ofHBr and an inert gas, such as in a mixture of HBr, N₂ and argon. Thehydrogen-based etch is typically conducted with a process gas that doesnot include oxygen-containing and fluorine-containing species. In someembodiments, the process gas consists essentially of one or morehydrogen-containing reactants and, optionally, an inert gas.

Hydrogen-based etch can selectively remove tin oxide in a presence ofthe following materials: silicon-containing compounds, such as SiO₂,SiN, SiC, SiOC, SiCN, SiON, SiCNO, spin on glass; metal oxides, such astitanium oxide, tungsten oxide, and zirconium oxide; metal nitrides,such as titanium nitride and tantalum nitride; metals, such as tungsten;photoresist and organic polymers. Further, hydrogen based etch can beused to selectively etch tin oxide in a presence of silicon oxidecovered silicon. Silicon oxide often forms on silicon surfaces whensilicon is exposed to atmosphere. Hydrogen-based etch can be also usedto selectively etch tin oxide in a presence of elemental silicon (e.g.,amorphous silicon), and carbon. Further, hydrogen-based etch can be usedto selectively etch tin oxide in a presence of metal carbides, andmaterials that contain metal and carbon. For example, tin oxide can beselectively etched with a hydrogen-based etch in a presence of atungsten carbon material (also referred to as tungsten-doped carbon). Insome embodiments, tungsten carbon material includes between about 20-60atomic % tungsten.

In some embodiments a semiconductor substrate is provided, where thesemiconductor substrate includes an exposed tin oxide layer and a layerof any of these materials. Next, tin oxide is selectively etched in apresence of these materials. These materials may be exposed prior tothis etch or may become exposed during the course of tin oxide etching.

The etch selectivity of the hydrogen-based etch in some embodiments isgreater than 10, such as greater than 30, e.g., greater than 50, orgreater than 80. The etch selectivity refers to the ratio of the etchrate of tin oxide to the etch rate of the other material for selectedprocess conditions. In some examples, etch selectivity of 100 wasachieved for etching tin oxide relative to SiO₂ with the use of H₂plasma.

The tin oxide etching methods that utilize hydrogen plasma (referring toa plasma formed in a hydrogen-containing reactant) can be implemented ina variety of apparatuses under a wide range of process conditions. Inone implementation the methods involve, providing a semiconductorsubstrate having an exposed layer of tin oxide to an etch chamber, andcontacting the substrate with a plasma formed in a process gascomprising H₂ (or another hydrogen-containing gas), and, optionally acarrier gas, such as helium or another inert gas. The term “etchchamber” or an “etching apparatus” refers to a chamber and an apparatusthat are configured for etching. In some embodiments the “etch chamber”or the “etching apparatus” are exclusively configured for etchingoperations. In other embodiments the “etch chamber” or “etchingapparatus” may be configured to perform other operations in addition toetching, such as, for example, deposition. For example, in someembodiments the etch chamber may also be used for ALD deposition.

In some embodiments the plasma used for in the hydrogen plasma etch isgenerated in the same process chamber that houses the semiconductorsubstrate. In other embodiments the plasma is generated remotely, and isintroduced into the process chamber that houses the substrate throughone or more inlets in the process chamber.

The etching is controlled such as to convert tin oxide to a volatile tinhydride. In one embodiment the H₂ content in the process gas is at least50% by volume, such as at least 80% by volume (can be up to andincluding 100%). In some embodiments, the process gas may furtherinclude a hydrocarbon, such as CH₄. In some embodiments, the process gasfurther includes Cl₂. For example, the process gas may consistessentially of H₂ and an inert gas (e.g., He), or the process gas mayconsist essentially of H₂, inert gas and a hydrocarbon (e.g., CH₄). Theetch is performed at a temperature of less than about 100° C., measurednear the substrate. The etch reaction, advantageously, generates onlyvolatile materials, such as SnH₄, which can be easily removed from theetch process chamber by evacuation and/or purging. The etch processtemperature is preferably selected to be less than about 100° C.,because higher temperatures can lead to decomposition of formed SnH₄ andto formation of particles that can contaminate the process chamber andthe substrate. The composition of the process gas and process conditionsare selected such as to reduce or eliminate formation of particlesduring the etch. Significantly, the etch reaction does not require anysignificant sputtering component, and can be performed in an absence ofexternal bias at the substrate, and in an absence of heavy ions (e.g.,argon ions). Reducing sputtering component can be beneficial forincreasing the etch selectivity relative to the second material on thesubstrate. Thus, in some embodiments etching is performed withoutproviding an external bias to the substrate and/or involves using helium(a light gas) as the carrier gas, in order to reduce sputtering.

Plasma for the hydrogen plasma etch can be generated using a variety offrequencies (low and high). Examples of suitable frequencies include 400KHz, 2 MHz, 13.56 MHz, 27 MHz or 2.45 GHz. Power used for plasmageneration can range in some embodiments, from between about 50 W to1,000 W corresponding to power density of between about 0.0018 and 0.36W/cm². The bias at the substrate is optional, and bias power can rangefrom about 0 to 500 W. Suitable gas flow rates per showerhead (forprocessing one 300 mm wafer) are:

H₂: 25 to 750 sccm;

Cl₂: 0 to 500 sccm (e.g., 5-200 sccm);

He: 0 to 500 sccm (e.g., 5-100 sccm); and

CH₄: 0 to 500 sccm (e.g., 5-100 sccm).

The etch process can be performed, in some embodiments, at a pressure ofbetween about 1 to 175 mTorr.

In some specific embodiments the plasma is generated using highfrequency generation (e.g., 13.56 MHz or 27 MHz), and it is providedusing plasma power of between about 200 to 500 W corresponding to powerdensity of 0.07 and 0.18 W/cm². The power for the bias at the substrateis between about 0 and 200 W. Suitable gas flow rates per showerhead(for processing one 300 mm wafer) are:

H₂: 100 to 300 sccm;

Cl₂: 0 to 200 sccm (e.g., 5-100 sccm);

He: 0 to 100 sccm (e.g., 5-50 sccm);

CH₄: 0 to 100 sccm (e.g., 5-50 sccm).

The etch process is performed in these embodiments at a pressure ofbetween about 1 to 30 mTorr.

It was discovered that the selectivity of the hydrogen-based etch can besignificantly increased by using carbon-containing reactants in theprocess gas that form a carbon-containing polymer (e.g. CH_(x) polymer)on the surface of the substrate during the etch. In some embodiments,the process gas used in this embodiment includes H₂ and a hydrocarbon(e.g., methane (CH₄)). The process gas typically also includes an inertgas. The ratio of H₂ to hydrocarbon, in some embodiments is preferablyat least 5, such as at least 10. In some embodiments the volume ratio ofH₂ to hydrocarbon is between about 5-500, such as about 10-300. In someembodiments selective etching of tin oxide in a presence of anothermaterial (or materials) includes exposing the substrate to a plasmaformed in a process gas comprising H₂ and a hydrocarbon (e.g., CH₄). Inone implementation H₂ is provided at a flow rate of between about100-500 sccm, and hydrocarbon is provided at a flow rate of betweenabout 1-20 sccm (such as between about 5-10 sccm). The process can beconducted using plasma power of between about 100-1,000 W, such asbetween about 200-500 W (for a single 300 mm wafer), corresponding topower densities of between about 0.14-1.3 W/cm², such as 0.28-0.71W/cm². In some implementations, the etch is conducted using a substratebias of between about 50-500 Vb, such as between about 100-200 Vb. Theprocess is preferably performed at a temperature of less than about 100°C. In one specific example the following gases are provided: H₂ at 100sccm; CH₄ at 5 sccm, and helium at 100 sccm. The plasma is formed in theprocess gas using a power of 300 W, and the substrate bias of 100 Vb at25% duty cycle is used. The process is performed at 30° C. and at apressure of 5 mTorr. The formation of carbon-containing polymer on asubstrate as described herein can increase the etch selectivity of tinoxide relative to any of the materials listed herein. This effect isparticularly useful when tin oxide is etched in a presence ofphotoresist, carbon, carbon-containing materials, and silicon (Si). Forexample, when the etching is conducted in a presence of photoresist, theetch selectivity can be greater than 100, and in some cases is nearlyinfinite. The use of this highly selective etch allows the use ofphotoresist of smaller thickness to lower photolithographic exposuredose and/or to prevent photoresist line collapse due to high aspectratio at small fine pitch. In the described method the CH_(x) polymerprotects the photoresist from being etched. Further this etch can beused to improve the geometry of the photoresist layer. In someembodiments, the tin oxide on a semiconductor substrate is selectivelyetched using this etch in a presence of a photoresist disposed above thetin oxide layer, and in a presence of a material that underlies tinoxide, with an etch selectivity of at least 10 relative to bothphotoresist and the material that underlies tin oxide. In someembodiments the material that underlies tin oxide includes one or moreof silicon (e.g., amorphous silicon), silicon-containing compound (e.g.,SiO₂, SiN, SiC, SiON, SiOC), carbon (e.g., amorphous carbon), and acarbon-containing compound (e.g., carbon tungsten).

In some embodiments, HBr is used as a hydrogen-containing reactant inthe hydrogen-based etch. In one implementation, the etching methodinvolves flowing HBr, and an inert gas (e.g., helium) at a flow rate of100-500 sccm and forming a plasma in this process gas using RF power of100-500 W (per one 300 mm wafer) corresponding to power densities of0.14-0.71 W/cm². This etch can be conducted with or without a substratebias. For example, substrate bias may be between 0-200 Vb, such as50-200 Vb. The process can be performed at a temperature of less than100° C. and a pressure of 5-50 mTorr.

Chlorine-based etch. In some embodiments selective tin oxide etching isperformed using a chlorine-based etch. Chlorine-based etch involvesexposing tin oxide to a chlorine-containing reactant (typically withplasma activation of the reactant) such that it converts tin oxide to atin chloride. SnCl₄ has a boiling point of 114° C. and can be removedfrom the process chambers. Examples of suitable chlorine-containingreactants include Cl₂, and BCl₃. Mixture of Cl₂ and BCl₃ is used in oneembodiment. Chlorine-based etching involves, in one implementation,forming a plasma in a process gas containing a chlorine-containingreactant, and, optionally, an inert gas, and contacting the substratewith the formed plasma. Chlorine-based etch can selectively remove tinoxide in a presence of the following materials: silicon-containingcompounds, such as SiO₂, SiN, SiC, SiOC, SiCN, SiON, SiCNO, spin onglass, carbon, and photoresist, although the selectivity forsilicon-containing material is typically lower than with ahydrogen-based etch. In some embodiments a semiconductor substrate isprovided, where the semiconductor substrate includes an exposed tinoxide layer and a layer of any of these materials. Next, tin oxide isselectively etched in a presence of these materials using thechlorine-based etch. These materials may be exposed prior to this etchor may become exposed during the course of tin oxide etching. In oneimplementation tin oxide is selectively etched in a presence of any ofthese materials using a BCl₃/Cl₂ etch. In one implementation, theetching method involves flowing BCl₃ at a flow rate of 5-100 sccm, Cl₂at a flow rate of 50-500 sccm and an inert gas (e.g., helium) at a flowrate of 100-500 sccm and forming a plasma in this process gas using RFpower of 100-500 W (per one 300 mm wafer) corresponding to powerdensities of 0.14-0.71 W/cm². This etch can be conducted with or withouta substrate bias. For example, substrate bias may be between 0-100 Vb,such as 10-100 Vb. The process can be performed at a temperature of lessthan 100° C. and a pressure of 5-50 mTorr.

In some embodiments chlorine-based etch is used to selectively etchcertain metal oxides in a presence of tin oxide. For example, titaniumoxide can be selectively etched in a presence of tin oxide usingchlorine-based etch. In some embodiments a semiconductor substrate isprovided, where the semiconductor substrate includes an exposed titaniumoxide layer and a layer of tin oxide. Next, titanium oxide isselectively etched in a presence of tin oxide using the chlorine-basedetch chemistry. Tin oxide may be exposed prior to this etch or maybecome exposed during the course of tin oxide etching.

Fluorocarbon-based etch. In some embodiments silicon-containingcompounds such as SiO₂, SiN, SiC, SiOC, SiCN, SiON, SiCNO, spin on glassare selectively etched in a presence of tin oxide using afluorocarbon-based etch. Fluorocarbon-based etch involves exposing thesilicon-containing compounds to plasma-activated fluorocarbons(C_(x)F_(y)) such that they are converted to volatile compoundscontaining Si—F bonds. Examples of suitable fluorocarbon reactantsinclude CF₄, C₂F₆ and the like. Fluorocarbon-based etching involves, inone implementation, forming a plasma in a process gas containing afluorocarbon, and, optionally, an inert gas, and contacting thesubstrate with the formed plasma. Fluorocarbon etch can selectivelyremove silicon-containing compounds in a presence of tin oxide. In someembodiments a semiconductor substrate is provided, where thesemiconductor substrate includes an exposed layer of asilicon-containing compound and a layer of tin oxide. Next, thesubstrate is contacted with a fluorocarbon plasma and thesilicon-containing compound is selectively etched in a presence of tinoxide. Tin oxide may be exposed prior to this etch or may become exposedduring the course of etching. Fluorocarbon-based etch is a type of afluorine-based etch.

Fluorine-based etch. In some embodiments elemental silicon andsilicon-containing compounds such as SiO₂, SiN, SiC, SiOC, SiCN, SiON,SiCNO, and spin on glass are selectively etched in a presence of tinoxide using a fluorine-based etch. Fluorine-based etch involves exposingthe silicon-containing material to a fluorine-containing reagent (e.g.,NF₃, SF₆, or a fluorocarbon), which is in some embodimentsplasma-activated, and converting the silicon-containing material to avolatile silicon fluoride. Tin oxide, however, does not form a volatilefluoride and therefore is not substantially etched by this chemistry. Inaddition to silicon-containing materials, titanium oxide, tungsten, andtungsten carbon can be selectively etched in a presence of tin oxideusing fluorine-based etches. Fluorine-based etching involves, in oneimplementation, forming a plasma in a process gas containing afluorine-containing reactant (e.g., NF₃), and, optionally, an inert gas,and contacting the substrate with the formed plasma. Fluorine-based etchcan selectively remove silicon-containing compounds and elementalsilicon in a presence of tin oxide. In some embodiments a semiconductorsubstrate is provided, where the semiconductor substrate includes anexposed layer of a silicon-containing compound and/or a layer ofelemental silicon (Si) and a layer of tin oxide. Next, the substrate iscontacted with a fluorine-containing reactant in a plasma and thesilicon-containing compound and/or Si is selectively etched in apresence of tin oxide. Tin oxide may be exposed prior to this etch ormay become exposed during the course of etching.

In one implementation silicon (Si) is selectively etched in a presenceof tin oxide using a fluorine-based etch. In one implementation, thisetching method involves flowing NF₃ at a flow rate of 5-100 sccm, Cl₂ ata flow rate of 50-500 sccm and an inert gas (e.g., nitrogen and/orhelium) at a flow rate of 100-500 sccm and forming a plasma in thisprocess gas using RF power of 100-1000 W (per one 300 mm wafer)corresponding to power densities of 0.14-1.4 W/cm². This etch can beconducted with or without a substrate bias. For example, substrate biasmay be between 0-100 Vb, such as 10-100 Vb. The process can be performedat a temperature of less than 100° C. and a pressure of 10-300 mTorr.

In some embodiments a semiconductor substrate is provided, where thesemiconductor substrate includes an exposed layer of a titanium oxide,tungsten, and/or tungsten carbon; and a layer of tin oxide. Next, thesubstrate is contacted with a fluorine-containing reactant in a plasmaand titanium oxide, tungsten, and/or tungsten carbon is selectivelyetched in a presence of tin oxide. Tin oxide may be exposed prior tothis etch or may become exposed during the course of etching.

In one implementation titanium oxide is selectively etched in a presenceof tin oxide using a fluorine-based etch. In one implementation, thisetching method involves flowing CF₄ at a flow rate of 5-500 sccm, CHF₃at a flow rate of 0-500 sccm (e.g., 10-500 sccm) and an inert gas (e.g.,argon) at a flow rate of 100-500 sccm and forming a plasma in thisprocess gas using RF power of 500-1000 W (per one 300 mm wafer)corresponding to power densities of 0.71-1.4 W/cm². This etch can beconducted with or without a substrate bias. For example, substrate biasmay be between 0-300 Vb, such as 10-300 Vb. The process can be performedat a temperature of less than 100° C. and a pressure of 5-50 mTorr.

In one implementation tungsten carbon is selectively etched in apresence of tin oxide using a fluorine-based etch. In oneimplementation, this etching method involves flowing NF₃ at a flow rateof 5-100 sccm, Cl₂ at a flow rate of 5-500 sccm and an inert gas (e.g.,argon and/or nitrogen) at a flow rate of 100-500 sccm and forming aplasma in this process gas using RF power of 100-1000 W (per one 300 mmwafer) corresponding to power densities of 0.14-1.4 W/cm². This etch canbe conducted with or without a substrate bias. For example, substratebias may be between 0-100 Vb, such as 10-100 Vb. The process can beperformed at a temperature of less than 100° C. and a pressure of 10-100mTorr.

Oxygen-based etch. In some embodiments one or more materials selectedfrom the group consisting of elemental carbon, carbon-containingcompounds, polymers, and photoresist is selectively etched in a presenceof tin oxide using an oxygen-based etch. Oxygen-based etch involvesexposing the materials listed above to an oxygen-containing reagent(e.g., O₂, O₃, SO₂, or CO₂), which is in some embodimentsplasma-activated, and converting the material to a volatile productcontaining carbon-oxygen bond (e.g., CO or CO₂). Oxygen-based etchinginvolves, in one implementation, forming a plasma in a process gascontaining an oxygen-containing reactant (e.g., O₂), and, optionally, aninert gas, and contacting the substrate with the formed plasma. In otherembodiments etching may occur in an absence of plasma. Oxygen-based etchcan selectively remove carbon (e.g., amorphous or diamond-like carbon),carbon-containing compounds, and photoresist in a presence of tin oxide.In some embodiments a semiconductor substrate is provided, where thesemiconductor substrate includes an exposed layer of one or morematerials selected from the group consisting of carbon, acarbon-containing compound and a photoresist, and a layer of tin oxide.Next, the substrate is contacted with an oxygen-containing reactant(optionally activated in a plasma) to convert carbon-containingmaterials to volatile CO or CO₂ thereby selectively etching them in apresence of tin oxide. Tin oxide may be exposed prior to this etch ormay become exposed during the course of etching.

Deposition of materials. Materials that are referenced herein can bedeposited using a variety of deposition methods, such as CVD (whichincludes PECVD), ALD (which includes PEALD), PVD (e.g., for depositionof metals and metal oxides), spin-on methods (e.g., for deposition ofcarbon, and some dielectrics). When conformal deposition is needed, ALDmethods are typically preferred.

SiO₂, SiC, SiN, SiOC, SiNO, SiCNO, and SiCN materials can be depositedusing a variety of methods, such as CVD, PECVD and ALD. The depositioncan include a reaction between a silicon-containing precursor and areactant (e.g., an oxygen-containing reactant, a nitrogen-containingreactant, or a carbon-containing reactant). A variety ofsilicon-containing precursors can be used for deposition of thesematerials, including silane, tetraalkylsilanes, trialkylsilanes,tetraethylorthosilicate (TEOS), etc. For example, SiO₂ may be depositedusing TEOS or silane as the silicon-containing precursor.

Carbon can be deposited by a CVD or PECVD method by using, for example,a hydrocarbon precursor (e.g., CH₄). In other implementations carbon maybe deposited by spin-on methods or by PVD. Photoresist and organicpolymers can be deposited, for example, by spin on methods.

The tin oxide layer is deposited by any suitable method such as by CVD(including PECVD), ALD (including PEALD), sputtering, etc. In someembodiments it is preferable to deposit the SnO₂ film conformally, suchthat it follows the surface of the substrate, including the surfaces ofany protrusions and recessed features on the substrate. One of thesuitable deposition methods of conformal SnO₂ film is ALD. Thermal orplasma enhanced ALD can be used. In a typical thermal ALD method, thesubstrate is provided to an ALD process chamber and is sequentiallyexposed to a tin-containing precursor, and an oxygen-containingreactant, where the tin-containing precursor and the oxygen containingreactant are allowed to react on the surface of the substrate to formSnO₂. The ALD process chamber is typically purged with an inert gasafter the substrate is exposed to the tin-containing precursor, andbefore the oxygen-containing reactant is admitted to the process chamberto prevent reaction in the bulk of the process chamber. Further, the ALDprocess chamber is typically purged with an inert gas after thesubstrate has been treated with the oxygen-containing reactant. Thesequential exposure is repeated for several cycles, e.g., between about10-100 cycles can be performed until the tin oxide layer having adesired thickness is deposited. Examples of suitable tin-containingprecursors include halogenated tin-containing precursors (such as SnCl₄,and SnBr₄), and non-halogenated tin-containing precursors, such asorganotin compounds, which include alkyl substituted tin amides and thelike. Specific examples of alkyl substituted tin amides that aresuitable for ALD are tetrakis(dimethylamino) tin,tetrakis(ethylmethylamino) tin,N²,N³-di-tert-butyl-butane-2,3-diamino-tin(II) and(1,3-bis(1,1-dimethylethyl)-4,5-dimethyl-(4R,5R)-1,3,2-diazastannolidin-2-ylidene.

Exemplary tin-containing precursor can be, or include, organotinprecursors such as, tetraethyl tin (SnEt₄), tetramethyl tin (SnMe₄),tetrakis(dimethylamino)tin (Sn(NMe₂)₄), tetrakis(diethylamido)tin(Sn(NEt₂)₄), tetrakis(ethylmethylamino)tin (Sn(NMeEt)₄),(dimethylamino)trimethyltin(IV) (Me₃Sn(NMe₂)), dibutyltin diacetate(Bu₂Sn(OAc)₂), Sn(II)(1,3-bis(1,1-dimethylethyl)-4,5-dimethyl-(4R,5R)-1,3,2-diazastannolidin-2-ylidene),N², N³-di-tert-butyl-butane-2,3-diamino-tin(II), and the like.Additional examples of organotin precursors include:bis[bis(trimethylsilyl)amino]tin(II)

where TMS is trimethylsilyl,

dibutyldiphenyltin

hexaphenylditin(IV)

tetraallyltin

tetravinyltin

tin(II) acetylacetonate

tricyclohexyltin hydride

trimethyl(phenylethynyl)tin

and

trimethylphenyltin

In another example, tin-containing precursors can also be inorganic tinprecursors, such as, tin halides (e.g., SnF₂, SnCl₄, SnBr₄), tinhydrides (e.g., SnH₄), and the like. In some embodiments chlorinatedorganotin precursors are used such as trimethyltin chloride

dimethyltin dichloride

and

methyltin trichloride

In some embodiments the tin-containing precursor is tetramethyl tin,tetrakis(dimethylamino)tin, or (dimethylamino)trimethyltin(IV).

Oxygen-containing reactants include without limitation oxygen, ozone,water, hydrogen peroxide, and NO. Mixtures of oxygen-containingreactants can also be used. The deposition conditions will varydepending on the choice of ALD reactants, where more reactive precursorswill generally react at lower temperatures than less reactiveprecursors. The processes typically will be carried out at a temperatureof between about 20-500° C., and at a subatmospheric pressure. Thetemperature and pressure are selected such that the reactants remain inthe gaseous form in the process chamber to avoid condensation. Eachreactant is provided to the process chamber in a gaseous form eitheralone or mixed with a carrier gas, such as argon, helium, or nitrogen.The flow rates of these mixtures will depend on the size of the processchamber, and are in some embodiments between about 10-10,000 sccm.

In one example the ALD process includes sequentially and alternatelyexposing the substrate in an ALD vacuum chamber to SnCl₄ (thetin-containing precursor) and deionized water (the oxygen-containingreactant) at a temperature of 200-400° C. In a specific example of anALD cycle, a mixture of SnCl₄ vapor with N₂ carrier gas is introducedinto the ALD process chamber for 0.5 seconds, and is then exposed to thesubstrate for 3 seconds. Next the ALD process chamber is purged with N₂for 10 seconds to remove SnCl₄ from the bulk of the process chamber, anda mixture of H₂O vapor with N₂ carrier gas is flowed into the processchamber for 1 second and is exposed to the substrate for 3 seconds.Next, the ALD process chamber is purged with N₂ and the cycle isrepeated. The ALD process is performed at subatmospheric pressure (e.g.,0.4 Torr) and at a temperature of 200-400° C.

While the use of halogenated tin precursors in ALD is suitable in manyembodiments, in some embodiments it is more preferable to usenon-halogenated organotin precursors to avoid corrosion problems thatmay occur with the use of halogenated precursors such as SnCl₄. Examplesof suitable non-halogenated organotin precursors include alkylaminotin(alkylated tin amide) precursors, such as tetrakis(dimethylamino) tin.In one example of an ALD process the substrate is sequentially exposedin an ALD chamber to tetrakis(dimethylamino) tin and H₂O₂ at atemperature of between about 50-300° C. Advantageously, the use of thisprecursor allows deposition of SnO₂ films at low temperatures of 100° C.or less. For example, SnO₂ films can be deposited at 50° C. without theuse of plasma to enhance reaction rate.

In some embodiments, SnO₂ films are deposited by PEALD. The same typesof tin-containing precursors and oxygen-containing reactants asdescribed above for thermal ALD can be used. In PEALD the ALD apparatusis equipped with a system for generating plasma in the process chamber,and for treating the substrate with the plasma. In a typical PEALDprocess sequence, the substrate is provided to the PEALD process chamberand is exposed to the tin-containing precursor which adsorbs on thesurface of the substrate. The process chamber is purged with an inertgas (e.g., argon or helium) to remove the precursor from the processchamber, and the substrate is exposed to an oxygen-containing reactantwhich is introduced into the process chamber. Concurrently with theintroduction of the oxygen-containing reactant or after a delay, plasmais formed in the process chamber. The plasma facilitates the reactionbetween the tin-containing precursor and the oxygen-containing reactanton the surface of the substrate that results in formation of tin oxide.Next, the process chamber is purged with an inert gas, and the cyclecomprising tin precursor dosing, purging, oxygen-containing reactantdosing, plasma treatment, and second purging is repeated as many timesas necessary to form a tin oxide film of desired thickness.

Tin Oxide as a Spacer

In some embodiments tin oxide layers are used as spacers. The use of tinoxide spacers is illustrated with reference to FIGS. 1A-1F, whichprovide schematic cross-sectional views of a semiconductor substrate atdifferent stages of processing. FIG. 2 provides a process flow diagramfor an embodiment of these methods.

Referring to FIG. 2 , the process starts in 201, by providing asubstrate having a plurality of protruding features. An illustrativesubstrate is shown in FIG. 1A, which shows two mandrels 101 residing onan etch stop layer (ESL) 103. The distance d1 between the neighboringmandrels is, in some embodiments, between about 10-100 nm. In someembodiments relatively larger distances of about 40-100 nm are used. Inother applications, the distance between closest mandrels is betweenabout 10-30 nm. The distance between the centers of closest mandrels,d2, which is also referred to as pitch, is, in some embodiments, betweenabout 30-130 nm. In some embodiments, the pitch is between about 80-130nm. In other embodiments, the pitch is between about 30-40 nm. Theheight of the mandrels d3 is typically between about 20-200 nm, such asbetween about 50-100 nm.

The materials of the mandrel and of the ESL are selected such as toallow subsequent selective etching of the mandrel material in thepresence of exposed tin oxide, and selective etching of the ESL materialin the presence of exposed tin oxide. Thus, the ratio of the etch rateof the ESL material to the etch rate of tin oxide is greater than 1,more preferably greater than about 1.5, such as greater than about 2 fora first etch chemistry. Similarly, the ratio of the etch rate of themandrel material to the etch rate of tin oxide is greater than 1, morepreferably greater than about 1.5, such as greater than about 2 for asecond etch chemistry.

In some embodiments the ESL material is a silicon-containing compound(e.g., SiO₂), or a metal oxide (e.g., titanium oxide, zirconium oxide,tungsten oxide). The mandrel material may include silicon-containingcompound (e.g., SiO₂, SiN, or SiC), a carbon-containing compound (e.g.,amorphous carbon, diamond-like carbon or photoresist), amorphous silicon(doped or undoped) and a metal oxide (TaO, TiO, WO, ZrO, HfO). In someembodiments the outer material of the mandrel may be different from themandrel core. For example, in some embodiments the mandrel is made ofamorphous silicon which is covered with silicon oxide (e.g., with aspontaneously formed layer of thermal oxide). The ESL layer and themandrels can be formed by one or more of physical vapor deposition(PVD), chemical vapor deposition (CVD), ALD (without plasma or by PEALD)or plasma enhanced chemical vapor deposition (PECVD) and the pattern ofthe mandrels can be defined using photolithographic techniques. Examplesof suitable ESL/mandrel combination include: (i) a silicon oxide ESL anda silicon oxide covered silicon mandrel; (ii) a silicon oxide ESL and acarbon-containing mandrel; (iii) a silicon oxide ESL and a metal oxidemandrel; (iv) a metal oxide ESL and a silicon oxide covered siliconmandrel; (v) a metal oxide ESL and a carbon-containing mandrel.

Referring again to the substrate shown in FIG. 1A, the ESL layer 103resides over and in contact with the target layer 105. The target layer105 is the layer that needs to be patterned. The target layer 105 may bea semiconductor, dielectric or other layer and may be made of silicon(Si), silicon oxide (SiO₂), silicon nitride (SiN), or titanium nitride(TiN), for example. In some embodiments the target layer is referred toas a hardmask layer and includes metal nitride, such as titaniumnitride. The target layer 105 may be deposited by ALD (without plasma orby PEALD), CVD, or other suitable deposition technique.

The target layer 105 resides over and in contact with layer 107, whichis in some embodiments a BEOL layer, that includes a plurality of metallines embedded into a layer of dielectric material.

Referring again to FIG. 2 , the process follows in 203 by depositing atin oxide layer over both the horizontal surfaces and sidewalls of theprotruding features. Referring to the structure shown in FIG. 1B, thetin oxide layer 109 is deposited over the ESL 103, and over the mandrels101, including the sidewalls of the mandrels. The tin oxide layer isdeposited by any suitable method such as by CVD (including PECVD), ALD(including PEALD), sputtering, etc. In some embodiments it is preferableto deposit the tin oxide film conformally, such that it follows thesurface of the layer 103 and the mandrels 101, as shown in FIG. 1B. Insome embodiments the tin oxide layer is deposited conformally to athickness of between about 5-30 nm, such as between about 10-20 nm. Oneof the suitable deposition methods of conformal tin oxide film is ALD.Thermal or plasma enhanced ALD can be used.

Referring to the process diagram of FIG. 2 , after the tin oxide layerhas been deposited, the process follows in 205 by completely removingthe tin oxide from the horizontal surfaces, without completely removingthe tin oxide layer from the sidewalls of the protruding features usinghydrogen-based etch or a chlorine-based etch. If the mandrels havesilicon-containing compounds or metal oxides as the outer layer ahydrogen-based etch can be used. If the outer layer of the mandrels is acarbon layer, chlorine-based etch can be used. The etch chemistryutilized in this step should be preferably selective to both the ESLmaterial and to the material of the outer layer of the mandrel, i.e.,the etch rate of tin oxide for this etch chemistry should be greaterthan the etch rate of the outer mandrel material and greater than theetch rate of the ESL material. Removal of tin oxide from horizontalsurfaces is illustrated by FIG. 1C. The tin oxide layer 109 is etchedfrom the horizontal surfaces over ESL 103 and over mandrels 101, withoutbeing fully etched from positions that adhere to the sidewalls ofmandrels 101. This etch exposes the layer 103 everywhere with theexception of locations near the sidewalls of the mandrels 101. Further,this etch exposes the top portions of the mandrels. The resultingstructure is shown in FIG. 1C. Preferably after this etch at least 50%,such as at least 80% or at least 90% of the initial height of the tinoxide layer at the sidewall is preserved. In one example tin oxide isselectively etched from a silicon oxide covered mandrel by ahydrogen-based etch (e.g., H₂ plasma etch) such that the outer materialof the mandrel (SiO₂) is exposed. Hydrogen-based etch is selective toSiO₂. In another example tin oxide is selectively etched from acarbon-containing (e.g., carbon) mandrel by a chlorine-based etch (e.g.,BCl₃/Cl₂ plasma etch) such that the carbon-containing material of themandrel is exposed. Such etch is selective to carbon-containingmaterials. In another example tin oxide is selectively etched from ametal oxide (e.g., titanium oxide) mandrel by a hydrogen-based etch(e.g., H₂ plasma etch) such that mandrel material (metal oxide) isexposed. This etch is selective to oxides of metals that do not formvolatile hydrides, such as titanium oxide.

In some embodiments, removal of the tin oxide layer from horizontalportions of the substrate involves using two steps with two differentchemistries. In a first step, referred to as the main etch, the bulk ofthe tin oxide layer is removed from horizontal surfaces typicallywithout fully exposing the underlying layers of mandrel and ESLmaterials. Etch chemistry of the main etch, therefore, in someembodiments, does not need to be selective. In some embodiments the mainetch is performed by treating the substrate with a chlorine-basedchemistry (e.g., BCl₃/Cl₂ plasma etch). After the main etch etchesthrough the SnO film or shortly before, the etching chemistry isswitched to an over etch chemistry. The endpoint for the main etch canbe detected by using an optical probe, which will signal when themandrel material or ESL material becomes exposed. Selective over etchchemistry is used to remove leftover tin oxide film withoutsubstantially etching the materials of mandrel and ESL and has beendescribed above. For example, a selective hydrogen-based etch or aselective chlorine-based etch may be used.

Next, mandrels 101 are removed from the substrate leaving exposed tinoxide spacers 101 and an exposed layer ESL 103, as shown in FIG. 1D.Removal of the mandrels is performed by exposing the substrate to anetch chemistry that selectively etches the mandrel material. Thus, theratio of the etch rate of the mandrel material to the etch rate of thetin oxide in this step is greater than 1, and is more preferably greaterthan 1.5. Further, the etch chemistry used in this step should, in someembodiments, selectively etch the mandrel material relative to ESLmaterial. A variety of etching methods can be used, and specific choiceof chemistry depends on the material of the mandrel and on the materialof the ESL layer. When the mandrel is made of amorphous silicon coveredwith silicon oxide, a fluorine-based chemistry (e.g., NF₃) or may beused to remove the silicon mandrels 101 together with the SiO₂ layercovering them. This chemistry is selective to tin oxide.

Another option for silicon mandrel removal is the use of a plasma formedin a mixture of HBr and O₂. In some embodiments, before the etch starts,the thin protective layer of silicon oxide is removed from the surfaceof silicon mandrels. This can be done by briefly exposing the substrateto a plasma formed in a process gas comprising a fluorocarbon. Afterremoval of the protective silicon oxide layer from the mandrels, thesilicon is selectively etched. In some embodiments, it is preferable touse a relatively small RF bias, or no external bias at all for thesubstrate in this step. If no external bias is used, the self bias ofthe substrate (10-20 V) is sufficient. Under no bias or low biasconditions, the HBr/O₂ plasma will selectively etch silicon in thepresence of tin oxide and silicon oxide. This etch can be performed in apresence of an ESL containing silicon-containing compounds.

When the mandrel is a carbon-containing material (e.g., carbon orphotoresist) the mandrel can be selectively removed using anoxygen-based etch. This chemistry is selective to tin oxide and can beused in a presence of ESL composed of silicon-containing compounds, andmetal oxide ESL.

When the mandrel is a metal oxide (e.g., titanium oxide, tungsten oxide,zirconium oxide, hafnium oxide, tantalum oxide) the substrate may betreated with a chlorine-based etch chemistry (e.g., BCl₃/Cl₂ in aplasma) to selectively remove the mandrel relative to tin oxide. Thischemistry can be used in a presence of an ESL containingsilicon-containing compounds (e.g., SiO₂, SiN, SiC).

Next, the exposed ESL film 103 is etched to expose the underlying targetlayer 105 at all positions that are not protected by the tin oxidespacers 109. The resulting structure is shown in FIG. 1E. The etchchemistry that is used in this step selectively etches the ESL materialin the presence of tin oxide. In other words, the ratio of the etch rateof the ESL material to the etch rate of tin oxide is greater than 1, andis more preferably greater than 1.5. The specific type of chemistry usedin this step will depend on the type of the ESL material. Whensilicon-containing compounds (e.g., silicon oxide and silicon oxidebased materials) are used, selective etching can be accomplished byexposing the substrate to a plasma formed in a process gas comprising afluorocarbon. For example, the ESL film can be etched by a plasma formedin a process gas comprising one or more of CF₄, C₂F₆, and C₃F₈. When theESL is a metal oxide layer (e.g., titanium oxide, tungsten oxide, orzirconium oxide), it can be etched selectively in a presence of tinoxide using a chlorine-based etch chemistry (e.g., BCl₃/Cl₂ in aplasma).

In the next step, the target layer 105 is etched at all positions thatare not protected by the ESL film 103, to expose the underlying layer107. The tin oxide spacers 109 are also removed in this etching stepproviding a patterned structure shown in FIG. 1F. In some embodiments,the etch chemistry used in this step is selected to remove both thetarget material and the tin oxide spacer material. In other embodiments,two different etching steps with different chemistries can be used topattern the target layer 105 and to remove tin oxide spacers 109respectively. A number of etching chemistries can be used depending onthe chemistry of the target layer. In one embodiment the target layer105 is a metal nitride layer (e.g., a TiN) layer. In this embodiment themetal nitride layer may be etched, and the tin oxide spacers can beremoved using a single etch chemistry by exposing the substrate to aplasma formed in a process gas comprising Cl₂ and a hydrocarbon (e.g.,CH₄). Generally, tin oxide spacers can be removed using any of tin oxideetching methods described above.

One of the problems encountered during formation of spacers is thefooting of the spacer, which is the difference between the width of thespacer at the bottom and the width of the spacer at the top. Ideally,the spacer should be straight, having substantially same width both attop and bottom. Tin oxide spacers have been compared to titanium oxidespacers experimentally. It was shown that with the use of H₂ plasma etchon tin oxide spacers, the footing can be significantly reduced to lessthan 1 nm. Titanium oxide, however, cannot be etched by H₂ plasma atall. When titanium oxide spacer was etched with an HBr/N₂/argon plasmaits footing was reduced only to 2.4 nm with the cost of greater spacerheight and CD loss.

Further the etch selectivity of ALD-deposited titanium oxide to thermalsilicon oxide (TOX) was demonstrated to be lower than the etchselectivity of ALD-deposited tin oxide to TOX for the HBr/N₂/argonplasma etch. Specifically, with this chemistry titanium oxide was etchedin a presence of TOX with a selectivity of about 10:1, whereas tin oxidewas etched with a selectivity of greater than 100:1. With H₂ plasmatitanium oxide was not etched at all, whereas tin oxide was etched in apresence of TOX with a selectivity of greater than 100:1. WithBCl₃/Cl₂/He plasma titanium oxide was etched with a selectivity of about5:1 (titanium oxide to TOX) whereas tin oxide was etched with aselectivity of about 4:1 (tin oxide to TOX). Hydrogen-based etchchemistries (both H₂-based and HBr-based) provide very high etchselectivities to silicon oxide of greater than 50:1 and greater than80:1 that cannot be achieved with titanium oxide.

In some embodiments, the methods described herein with reference toFIGS. 1A-1F and 2 are modified and involve the use of a passivationlayer over tin oxide layer at the sidewalls of the mandrels. The purposeof the passivation layer is to minimize etching of tin oxide at thesidewalls during the step of tin oxide removal from horizontal surfaces.In an absence of the passivation layer, the tin oxide at the sidewallsmay be inconsistently etched in a lateral direction, which may lead tospacer critical dimension (CD) variation. The use of a passivation layercan prevent or minimize this lateral etch and result in a moreconsistent distance between spacers. In addition, the use of apassivation layer can prevent the erosion of top corners of the spacersthereby leading to spacers with more rectangular shapes. Further, theuse of a passivation layer at the sidewalls allows for more facile etchof the bottom slope or footing of the tin oxide layer as there would bemore available etching species (e.g., ions in a plasma) being drivendownward by a bias at the substrate. The passivation layer mayeventually be consumed partially or completely in subsequent etchingsteps so that the spacer CD can be maintained.

The material of the passivation layer is selected such that it is moreresistant to a particular etch chemistry that is being used for theremoval of tin oxide from horizontal surfaces. In some embodiments, thepassivation material is a silicon-containing compound such as SiO₂, SiN,or SiC, which can be deposited, for example by PECVD. In otherembodiments the passivation material is carbon (e.g., deposited using ahydrocarbon precursor), as described herein. In other embodiments, thepassivation material is a tin-containing compound, such as tin nitride(SnN), tin bromide (SnBr), or tin fluoride (SnF). In some embodimentsthese compounds are formed by converting an outer portion of tin oxideto the tin-containing passivation material. For example, tin oxide canbe converted to tin nitride by exposing the substrate to anitrogen-containing compound in a plasma (e.g., N₂ plasma). Tin bromidemay be formed by exposing the substrate to a bromine-containing compound(e.g. HBr). Tin fluoride may be formed by exposing the substrate to afluorine-containing compound in a plasma (e.g., NF₃ plasma orfluorocarbon plasma). The conditions during SnBr and SnF deposition areadjusted such as to minimize etching. For example, the reaction may becarried out without biasing the substrate or with low bias to minimizeremoval of SnBr and SnF. The passivation layer is typically formed to athickness of about 1-5 nm.

FIGS. 3A-3E provide schematic cross-sectional view of a portion of thesubstrate during processing using passivation layer. FIG. 4 provides aprocess flow diagram for such process. Referring to FIG. 4 , the processstarts in 4401 by providing a substrate having a plurality of protrudingfeatures and proceeds in 4403 by depositing tin oxide on sidewalls andhorizontal surfaces of the protruding features, in the same way as itwas described with reference to FIGS. 1A and 1B. The substrate shown inFIG. 1B is also illustrated in FIG. 3A, where the target layer is layer301, the ESL is 303, the mandrel is 305, and the tin oxide layer is 307.The materials of the layers generally may be the same as in theembodiment described with reference to FIGS. 1A-1F. In the embodimentillustrated in FIG. 3A the mandrel 305 is a silicon (Si) mandrel havingan outer layer of silicon oxide (SiO₂) 302, but it is understood thatthe described process sequence can be used with a variety of mandrelmaterials including carbon-containing mandrels and metal oxide mandrels.Referring to FIG. 4 , after the tin oxide layer has been deposited, theprocess follows in 4405 by forming a passivation layer over the tinoxide layer at the sidewalls of the protruding features. The resultingstructure is shown in FIG. 3B, which shows the passivation layer 309 onthe sidewalls of the protruding feature. In the depicted embodiment thepassivation layer is not present on the horizontal surfaces.

Such passivation layer can be formed in some embodiments by first (a)conformally depositing the passivation material (e.g., silicon oxide,silicon nitride, silicon carbide, or carbon) over both the sidewalls andthe horizontal surfaces of the mandrel and then (b) completely removingthe passivation layer from horizontal surfaces without completelyremoving the passivation layer from the sidewalls (e.g., such that atleast 50, or at least 80% of the passivation layer material at thesidewall remains after etch).

When the passivation material is a silicon-containing compound, it canbe etched from the horizontal surfaces using a fluorocarbon-based etchselectively to tin oxide. When the passivation material is acarbon-containing material it can be removed from horizontal surfacesusing an oxygen-based etch selectively to tin oxide, or using a shortexposure to a plasma formed in a hydrogen-containing gas (e.g. H₂).Tin-containing passivation materials, in some embodiments are removedfrom horizontal surfaces using the same chemistry as used for tin oxideetching, with the use of a sufficient bias at the substrate thatfacilitates removal of material from horizontal surfaces. For example,the process may start with a plasma etch with a first bias to removetin-containing passivation material from the horizontal surfaces andthen the bias may be reduced or turned off as the process transfers tomain tin oxide etch. In some embodiments a chlorine-based chemistry(e.g., BCl₃/Cl₂ plasma) is used during etching of passivation materialand tin oxide from the horizontal surfaces.

Next, referring to operation 4407 the process follows by completelyremoving tin oxide from the horizontal surfaces of the mandrel withoutcompletely removing the tin oxide at the sidewalls of the mandrel. Thisetch can be performed using any of the suitable tin oxide etchchemistries described herein, such as using a hydrogen-based etch (e.g.,H₂ plasma), a chlorine-based etch (e.g., Cl₂ and/or BCl₃ in a plasma),HBr plasma etch or any combination of these etches. In the embodimentdepicted in FIGS. 3C and 3D this etch is performed in two steps. In afirst step, the bulk of the tin oxide is etched from horizontal surfacesusing a chlorine-based etch (e.g., BCl₃ and Cl₂ in a plasma) to providea structure shown in FIG. 3C, where the structure has an exposed siliconoxide outer mandrel material at the top of the mandrel and an excess oftin oxide at the bottom corners of the mandrel. Next, the excess tinoxide is etched with a hydrogen-based overetch chemistry (e.g., H₂ in aplasma) providing a structure shown in FIG. 3D. Next the mandrelmaterial is selectively etched and removed, as was previously describedwith reference to FIGS. 1A-1F, leaving the spacers 307. In the depictedembodiment the mandrel etch chemistry also removes the passivation layer309, leading to a structure shown in FIG. 3E. Subsequent processing ofthe ESL can follow as was previously described with reference to FIGS.1D-1F.

In one more specific example, layer 301 is TiN, the ESL 303 is a siliconoxide layer; the mandrel 305 is silicon (Si) covered with silicon oxideouter layer 302, and layer 307 is tin oxide. In reference to thisexample, the processing method includes: providing a substrate having asilicon oxide layer, and a plurality of silicon protrusions, where thesilicon protrusions are covered with native silicon oxide, followed bydepositing a tin oxide layer conformally over the substrate (e.g., byALD) and forming a silicon oxide passivation layer (e.g., 1-2 nm thick)only over tin oxide on the sidewalls of the protruding features. Afterthe passivation layer was formed, the method follows by etching tinoxide from horizontal surfaces without completely removing tin oxideresiding at the sidewalls of the protruding features. In this example,the etching is conducted using a main (bulk) etch (e.g., Cl₂/BCl₃ plasmaetch) followed by overetch, where the overetch may be, for example ahydrogen plasma etch that is used to reduce footing. After etching themethod continues by removing the silicon mandrels without removing thetin oxide spacers. It is noted that the silicon oxide passivation layeron the sidewalls can be formed by first conformally depositing siliconoxide over tin oxide (e.g., by PECVD, or ALD), and then selectivelyetching silicon oxide from horizontal surfaces (e.g., by fluorocarbonplasma). This sequence was experimentally tested using BCl₃/Cl₂ plasmamain etch followed by H₂ plasma overetch for tin oxide removal fromhorizontal surfaces. In this experimentally tested example, after themain etch, the critical dimension loss was zero nm; the footing wasabout 6 nm, and the amount of etch into silicon oxide ESL is zero nm.After the overetch, the critical dimension loss, the footing, and theamount of etch into silicon oxide ESL were all zero nm.

In another specific example, tin nitride formed from an outer portion ofthe tin oxide is used as a passivation material. In some embodiments, itis preferable to passivate the sidewalls of tin oxide using a tinnitride passivation layer during formation of tin oxide spacers, andthereby reduce the variation in the spacer. In some embodiments themethod includes: (a) providing a substrate having a silicon oxide layer,and a plurality of silicon protrusions, where the silicon protrusionsare covered with native silicon oxide; (b) depositing a tin oxide layerconformally over the substrate (e.g., by ALD); (c) forming a thin tinnitride passivation layer only over tin oxide on the sidewalls of theprotruding features; (d) etching tin oxide from horizontal surfaceswithout completely removing tin oxide residing at the sidewalls of theprotruding features (e.g., using a combination of a main (bulk) etch(e.g., Cl₂/BCl₃ etch) and overetch, where the overetch may be, forexample hydrogen plasma etch that is used to reduce footing); and (e)removing the silicon mandrels without removing the tin oxide spacers.The tin nitride passivation layer on the sidewalls can be formed byfirst conformally forming the passivation layer over the entire tinoxide layer, followed by selectively removing tin nitride fromhorizontal surfaces. In some embodiments tin nitride layer is formed bytreating the exposed tin oxide layer with a nitrogen-containing plasma.For example, the plasma may be formed in a nitrogen-containing gas, suchas N₂ or NH₃. The plasma may be direct (formed in the same chambercompartment that houses the substrate) or remote (formed in a differentchamber or chamber compartment and fed to the compartment housing thesubstrate). In some embodiments this nitridation treatment is performedin the same process chamber that is used for tin oxide layer deposition.In other embodiments, nitridation is performed in a different chamber.In some embodiments, the nitridizing plasma treatment is performed forless than about 5 seconds. Another method for forming a conformal layerof tin nitride is deposition of tin nitride over the conformal tin oxidelayer. Tin nitride can be deposited, for example, by ALD or CVD. In someembodiments, ALD deposition involves contacting the substrate with atin-containing precursor and forming a tin-containing layer on thesurface of the substrate, followed by treatment with anitrogen-containing plasma, where the process is repeated as many timesas necessary to build a passivation layer of desired thickness. Afterthe conformal tin nitride layer has been formed, tin nitride is etchedfrom horizontal surfaces leaving tin nitride only on the sidewalls. Insome embodiments, the chemistry of this etch is the same as thechemistry of the main etch, but it is carried out using substrate bias,such that it is more vertically anisotropic than the main etch. Forexample, tin nitride can be removed from horizontal surfaces usingCl₂/BCl₃ plasma etch with substrate bias. Next, the Cl₂/BCl₃ main etchfollows (e.g., with no substrate bias or with lower bias than that usedduring tin nitride removal from horizontal surfaces), which is thenfollowed by H₂ overetch. Tin nitride provides an excellent protection totin oxide at the sidewalls during the main etch process. The use of tinnitride as a passivation layer has been experimentally tested and it wasconfirmed that the thickness of tin oxide on the sidewalls of mandrelsis greater in those cases, where tin nitride passivation layer was used,than in identical structures processed without tin oxide nitridation.

Hardmask Applications

In some embodiments, tin oxide films are used as hardmasks. Tin oxidehardmasks can be patterned such as to form a substrate having recessedfeatures, where there is an exposed material at the bottoms of therecessed features. The substrate then can be processed in a presence ofthe tin oxide hardmask. In some embodiments processing involves etchingthe material exposed at the bottoms of the recessed features. In otherembodiments, processing may involve depositing a material into therecessed features. In other embodiments, processing may involvechemically modifying the material exposed at the bottoms of the recessedfeatures.

Patterned tin oxide layers can be formed using a variety of methods. Inone embodiment patterned tin oxide film is formed usingphotolithographic patterning. The method involves, in one embodiment,providing a substrate having a blanket tin oxide layer formed on asubstrate and forming a patterned photoresist layer over the blanket tinoxide layer. The patterned photoresist layer over the tin oxide layer insome embodiments is formed directly on top of and in contact with thetin oxide layer. In other embodiments, there may be one or moreintermediate hardmask layers between the layer of tin oxide andphotoresist. After the photoresist layer has been deposited andpatterned using standard photolithographic techniques, the pattern fromthe photoresist is transferred onto the tin oxide layer, i.e. theexposed tin oxide layer is etched. In some embodiments the tin oxidelayer is etched in a presence of exposed photoresist using a selectiveetch, such as a hydrogen-based etch (e.g., H₂ in a plasma). Whenintermediate hardmasks are present between the layer of tin oxide andphotoresist, the pattern from the photoresist is first transferred tothese intermediate hardmasks (e.g., mask containing a silicon-containingcompound such as spin-on glass, or a carbon mask) and then to tin oxide.In some embodiments the tin oxide layer is etched in a presence ofanother intermediate hardmask material (e.g., a silicon-containingcompound or carbon) using a suitable selective chemistry, such ashydrogen-based etch and/or chlorine-based etch.

FIGS. 5A-5C illustrate schematic cross-sectional views of a substrateundergoing processing with a tin oxide mask. FIG. 6 provides a processflow diagram for processing the substrate with a tin oxide hardmask. Inoperation 601, a substrate having patterned tin oxide layer is provided.The tin oxide layer may be patterned using photolithographic techniquesas described above or using the process sequence that is used to formtin oxide spacers, that was described with reference to FIG. 1A-1D. Anexample of such substrate is shown in FIG. 5A, where the substrateincludes a sublayer 51, and a layer 53, which resides between thesublayer 51 and the patterned tin oxide layer 55. The exposed portion ofthe substrate includes recessed features formed in the tin oxide layer55. The material of layer 53 is exposed at the bottoms of the recessedfeatures. While in the depicted embodiment there is no additionalmaterial on the top of patterned tin oxide layer 55, in otherembodiments there may be photoresist or material from intermediatehardmasks present on top of tin oxide 55.

Next, in operation 603, the substrate is processed in a presence of thetin oxide layer 55. Processing may involve, for example, etching of theexposed material 53, deposition of material into the recessed features,or chemical modification of the exposed material 53. Etching of material53 is illustrated in FIG. 5B, where recessed features defined by thepattern of the tin oxide layer 55 are formed in layer 53. A variety ofselective etch chemistries can be used for etching the material of layer53 in a presence of tin oxide 55. For example, when layer 53 is asilicon-containing material, it may be selectively etched in a presenceof tin oxide using a fluorine-based chemistry. For example,silicon-containing compounds, such as silicon oxide, silicon nitride andsilicon carbide can be etched using a fluorocarbon plasma chemistry.When layer 53 is a carbon-containing layer (e.g., amorphous carbon), itmay be selectively etched using an oxygen-based chemistry, as describedherein. When layer 53 is a metal oxide layer (e.g., titanium oxide,zirconium oxide, tantalum oxide, hafnium oxide), it may be selectivelyetched in a presence of tin oxide using a chlorine-based chemistry, asdescribed herein (e.g., BCl₃/Cl₂ in a plasma). The material of thesublayer 51 is different from the material of layer 53, and layer 51 isnot substantially etched during the etching of layer 53. The resultingstructure, shown in FIG. 5B has recessed features formed in layer 55 and53 and an exposed material of sublayer 51 at the bottoms of the recessedfeatures.

Next, in operation 605 the tin oxide material 55 is removed providing astructure shown in FIG. 5C, where a patterned layer 53 resides oversublayer 51. In some embodiments, this sequence is further used topattern sublayer 51, which is in some embodiments a SiN layer, a metalnitride (e.g., TiN, or TaN), or metal layer. Removal of tin oxide ispreferably performed using a chemistry that is selective to both thematerial of layer 53 and layer 51. For example, when these materials aresilicon-containing materials, carbon-containing materials, metal oxides,metal nitrides, or metals a selective hydrogen-based etch (e.g., H₂plasma etch may be used). Further, in some embodiments when materials oflayer 53 and 51 are silicon-containing materials or carbon-containingmaterials a chlorine-based etch (e.g., BCl₃/Cl₂ in a plasma) may beemployed.

In one specific example of a process flow that uses a tin oxidehardmask, the sublayer 51 is a SiN layer, or a metal layer, and layer 53is silicon oxide. The process starts by providing a planar substratehaving an exposed layer of silicon oxide over the SiN or metal layer 51.Next, a blanket tin oxide layer is deposited over silicon oxide, and tinoxide is then patterned (e.g., using photolithographic patterning),leading to a structure shown in FIG. 5A. Next, exposed silicon oxide isselectively etched relative to tin oxide, for example, usingfluorocarbon plasma, leading to a structure shown to FIG. 5B. Next, tinoxide is stripped (removed), for example, using a hydrogen plasma etch,leading to a structure shown in FIG. 5C.

Tin Oxide Middle Layer.

In another hardmask implementation, tin oxide is used as an intermediatehardmask (middle layer) for patterning of a carbon layer or anothermaterial. In one embodiment, a substrate is provided, where thesubstrate includes a patterned layer of tin oxide formed on acarbon-containing layer (e.g., on an amorphous carbon layer), whereinthe substrate includes a plurality of recessed features having anexposed carbon-containing material at the bottoms of the recessedfeatures. Next the exposed carbon-containing material is selectivelyetched in a presence of tin oxide to form recessed features in thecarbon-containing layer. Suitable selective etch chemistries includehydrogen-based etch chemistry (e.g., H₂ in a plasma, and HBr in aplasma) and chlorine-based etch chemistry (e.g., BCl₃ and/or Cl₂ in aplasma). One suitable process sequence is illustrated by cross-sectionalsubstrate views shown in FIGS. 5D-5G. The substrate shown in FIG. 5Dincludes a sublayer 51 (e.g., amorphous silicon or any of the targetlayers described herein), a blanket layer 53 of a carbon-containingmaterial (e.g., amorphous carbon) residing over sublayer 51 and ablanket tin oxide layer 55 residing over carbon-containing layer 53. Thesubstrate further includes a patterned photoresist layer 57 over the tinoxide layer 55, and an underlayer 56 between the photoresist 57 and thetin oxide layer 55, where the underlayer may be, for example, spin onglass. The underlayer 56 is exposed at the bottoms of the recessedfeatures formed in the patterned photoresist layer 57 on the surface ofthe substrate. The pattern of the photoresist is transferred to theunderlayer 56, by selectively etching the underlayer in a presence ofphotoresist, e.g., by a fluorocarbon-based plasma etch. The etch exposesthe tin oxide layer 55 at the bottoms of the recessed features, as shownin FIG. 5E. Next, tin oxide is patterned using an etch that ispreferably selective to the underlayer material. For example, tin oxidemay be etched using a hydrogen-based etch or a chlorine-based etch. Inthe resulting structure shown in FIG. 5F, the pattern has beentransferred from photoresist to the tin oxide layer and thecarbon-containing layer 53 is exposed at the bottoms of recessedfeatures. Next, the process follows by etching the exposedcarbon-containing layer 53. Preferably, a chemistry that is selective totin oxide is used. For example, the exposed carbon-containing layer 53may be etched by an oxygen-based etch (e.g., carbon can be etched by aplasma formed in an oxygen-containing gas). The remaining photoresistand underlayer 56 may also be removed in this step. The structureobtained after this etch is shown in FIG. 5G. The process may furtherfollow by removal of tin oxide 55 and subsequent processing of theexposed sublayer 51.

Another implementation of the middle layer embodiment is shown in FIGS.5H-5K. The sequence is similar to the one described with reference toFIGS. 5D-5G, but is performed without an underlayer 56. In this sequencethe patterned photoresist 57 is formed directly on the tin oxide layer55, which is followed by tin oxide etch in a presence of photoresist(e.g., using a hydrogen-based etch (H₂ or HBr)) or a chlorine-basedetch. The process then follows to transfer the pattern from the tinoxide middle layer 55 to the carbon-containing layer 53, where the layer53 may itself serve as a hardmask for patterning the underlying layer51. Next, the tin oxide 55 is selectively etched and removed in apresence of carbon-containing layer 53, e.g., using a hydrogen-basedetch chemistry (e.g., H₂ in a plasma). These middle layer sequences aresuitable for EUV hardmask processing applications.

In another embodiment, a highly selective etch is used to transfer thephotoresist pattern to the tin oxide layer. For example tin oxide can beelectively etched in a presence of overlying photoresist and anunderlying material using a hydrogen-based etch chemistry, with anaddition of a carbon-containing reactant, where the carbon containingreactant is used to form a carbon-containing polymer on the surface ofthe substrate and increase etch selectivity. For example, plasma may beformed in a mixture of H₂, hydrocarbon (e.g., CH₄), and, optionally aninert gas, as described herein. This will be illustrated with referenceto FIGS. 5H-5K. In this example, as shown in FIG. 5H, a patterned layerof photoresist 57 is formed over the tin oxide layer 55 (e.g., 9-12 nmthick). The layer of material directly underlying the tin oxide layer,in this illustration, is a tungsten carbon layer 53 (35-55 nm thick).The layer 51 in this illustration is silicon oxide (e.g., TEOS cap),which may reside on a layer of extreme low k dielectric used in BEOLprocess sequence. First, tin oxide is selectively etched in a presenceof the photoresist and tungsten carbon using the highly selective H₂/CH₄plasma etch. The recessed features are formed and the tungsten carbonlayer is exposed, as shown in FIG. 5I. Next, tungsten carbon isselectively etched in a presence of tin oxide, exposing the underlyingTEOS layer. For example, tungsten carbon can be etched selectivelyrelative to tin oxide using an NF₃/Cl₂ plasma etch described herein. Thephotoresist may also be substantially removed during this step. Theresulting structure is shown in FIG. 5J. Next, the tin oxide is removedfrom the substrate using an etch that is selective to carbon tungsten.In some embodiments it is preferable to remove tin oxide using H₂plasma. In some embodiments hydrocarbon additives are not used duringthis step. For example tin oxide can be removed after the underlyinglayer has been etched using H₂ etch under the following processconditions. In this example the etch involves flowing H₂ at a flow rateof 100-500 sccm, and forming a plasma in this process gas using RF powerof 100-500 W (per one 300 mm wafer). This etch can be conducted with orwithout a substrate bias. For example, substrate bias may be between0-100 Vb, such as 10-100 Vb. The process can be performed at atemperature of less than 100° C. and a pressure of 5-50 mTorr.

Another process flow with a tin oxide middle layer hardmask isillustrated by the cross-sectional views in FIGS. 5L-5O. In thisexample, as shown in FIG. 5L, a patterned layer of photoresist 57 isformed over the tin oxide layer 55 (e.g., 9-12 nm thick). The layer ofmaterial directly underlying the tin oxide layer, in this illustration,is an amorphous silicon (Si) layer 53 (35-55 nm thick). The layer 51 inthis illustration is a silicon oxide etch stop layer. In thisillustration the photoresist is deposited such that it is wider at thebottom than at the top. It was shown that with the use of theH₂/hydrocarbon plasma etch it is possible to reduce the difference inphotoresist width and make it substantially rectangular incross-section. First, tin oxide is selectively etched in a presence ofthe photoresist and amorphous silicon using the highly selective H₂/CH₄plasma etch. The recessed features are formed and the amorphous siliconlayer is exposed, while the geometry of photoresist is improved, asshown in FIG. 5M. Next, silicon is selectively etched in a presence oftin oxide, exposing the underlying etch stop layer. For example, siliconcan be etched selectively relative to tin oxide using NF₃/Cl₂ plasmaetch described herein. The etch selectivity of greater than 40 (siliconto tin oxide) can be achieved with this etch. The photoresist may alsobe partially removed during this step. The resulting structure is shownin FIG. 5N. Next, the tin oxide is removed from the substrate using anetch that is selective to silicon. In some embodiments it is preferableto remove tin oxide using H₂ plasma. The remaining photoresist 57 can beremoved during H₂ plasma treatment. The resulting structure is shown inFIG. 5O.

The use of tin oxide as a hardmask is highly advantageous because it canbe etched with very high selectivity relative to silicon oxide, which isa common layer to be patterned. It can also be selectively etched with adry plasma etch chemistry (e.g., hydrogen-based or chlorine-basedchemistry) to a wide variety of other materials, including carbon,photoresist, metals, metal nitrides, and metal oxides. Tin oxidehardmasks also compare favorably to titanium nitride hardmasks becausetin oxide does not require wet etching and can be etched with hydrogenplasma, whereas titanium nitride is typically removed by wet etchingmethods.

Reverse tone hardmasks. In some embodiments, tin oxide is used invarious reverse tone hardmasks applications. One exemplary process flowis shown in FIG. 8 and is illustrated by schematic cross-sectional viewsof a substrate in FIGS. 7A-7C. The process starts in 801 by providing asubstrate having an exposed patterned ashable layer and a plurality ofrecessed features. Examples of ashable materials includecarbon-containing materials such as amorphous carbon, diamond-likecarbon, photoresist and organic polymers where the polymers may beundoped or doped with metals or metal oxides. The patterned layer ofashable material can be formed, for example, by depositing a blanketlayer of ashable material (e.g., by PECVD or a spin on method), followedby photolithographic patterning. FIG. 7A illustrates a substrate havinga patterned layer of ashable material 703 residing on a sublayer 701(e.g., Si, SiN, metal nitride or any target or sublayer materialdescribed herein). There is a plurality of recessed features on thesubstrate and layer 701 is exposed at the bottoms of the recessedfeatures. Next, in operation 803, the recessed features on the substrateare filled with tin oxide (e.g., using CVD). An overburden is alsotypically formed over the layer of the ashable material 703 in thisstep. The obtained structure is shown in FIG. 7B, where the depositedtin oxide 705 fills the gaps between the ashable material 703 and formsan overburden. The overburden can then be removed, e.g, by a chemicalmechanical polishing (CMP) operation or a bulk plasma etch (e.g., usinga hydrogen-based and/or chlorine-based plasma etch) to expose theashable material 703. After planarization, in operation 805, the ashablematerial is removed without substantially removing the tin oxidematerial (e.g., at least 90% of tin oxide remains) thereby forming acomplementary pattern of tin oxide 705 as shown in FIG. 7C.

In one specific example, a substrate containing a patterned carbon layerresiding on a target layer (e.g., silicon oxide, silicon nitride or ametal) is provided. The patterned carbon layer has a plurality ofrecesses (e.g., with widths of between about 5-50 nm). Next, therecesses are filled with tin oxide and a tin oxide overburden is formed(e.g., CVD). Next, tin oxide overburden is removed (e.g., by CMP or adry plasma etch that is selective to carbon) to expose carbon, and thenthe carbon is removed (stripped) e.g., using O₂ plasma, withoutcompletely removing the tin oxide.

Another embodiment of a reverse tone mask implementation is shown in aprocess flow diagram in FIG. 10 and is illustrated by schematiccross-sectional view of the processed substrate in FIGS. 9A-9C. Theprocess starts in 1001 by providing a substrate having a patterned tinoxide layer and a plurality of recessed features. This is illustrated inFIG. 9A, where the patterned tin oxide layer 903 resides on a sublayer901 (e.g., metal nitride, or metal layer), The sublayer 901 is exposedat the bottoms of the recessed features formed in the tin oxide layer903. Next, in operation 1003, the recessed features are filled by asilicon-containing material, e.g., by CVD. Examples of suitablesilicon-containing materials include silicon (e.g., amorphous silicon orpolysilicon) and silicon-containing compounds, such as silicon oxide,silicon nitride, and silicon carbide. An overburden over the tin oxidelayer may be formed during this deposition. The resulting structure isshown in FIG. 9B, where the silicon-containing material 905 fills thegaps in the patterned tin oxide layer and forms an overburden. Next, theoverburden is removed by CMP or by a plasma etch (e.g., a fluorine-basedetch, such as a fluorocarbon plasma etch) and the tin oxide 903 isexposed. In the next operation 1005 the tin oxide is removed withoutremoving the silicon-containing material thereby forming a patternedlayer of silicon-containing material (reverse tone or complementarypattern to the tin oxide pattern). The tin oxide is etched selectivelyto the silicon-containing material, for example, using a hydrogen-basedetch (e.g., H₂ plasma etch, or HBr plasma etch) or a chlorine-based etch(e.g., BCl₃/Cl₂ etch). The structure obtained after the etch is shown inFIG. 9C, where the patterned silicon-containing layer 905 is shown. Thesublayer 901 is exposed at the bottoms of the recessed features formedin the silicon-containing material 905.

In one implementation, a substrate having a target layer with apatterned layer of tin oxide over the target layer, is provided. Next,the recessed features in the patterned tin oxide are filled with siliconoxide, and a silicon oxide overburden is formed (e.g., by PECVD). Next,the silicon oxide overburden is etched (recess etched) to expose tinoxide, and then tin oxide is removed (stripped), e.g., using hydrogenplasma, thereby leaving patterned silicon oxide with a pattern that iscomplementary to the initial tin oxide pattern.

Apparatus

The etching methods described herein can be carried out in a variety ofapparatuses. A suitable apparatus includes an etch process chamber, asubstrate holder in the etch process chamber configured to hold thesubstrate in place during etching, and a plasma generating mechanismconfigured for generating a plasma in a process gas.

Examples of suitable apparatuses include inductively coupled plasma(ICP) reactors which, in certain embodiments, may also be suitable forcyclic deposition and activation processes, including atomic layeretching (ALE) operations and atomic layer deposition (ALD) operations.Although ICP reactors are described herein in detail, it should beunderstood that capacitively coupled plasma reactors may also be used.

FIG. 11 schematically shows a cross-sectional view of an inductivelycoupled plasma integrated etching and deposition apparatus 400appropriate for implementing plasma etching described herein, an exampleof which is a Kiyo® reactor, produced by Lam Research Corp. of Fremont,CA The inductively coupled plasma apparatus 400 includes an overallprocess chamber 424 structurally defined by chamber walls 401 and awindow 411. The chamber walls 401 may be fabricated from stainless steelor aluminum. The window 411 may be fabricated from quartz or otherdielectric material. An optional internal plasma grid 450 divides theoverall process chamber into an upper sub-chamber 402 and a lowersub-chamber 403. In most embodiments, plasma grid 450 may be removed,thereby utilizing a chamber space made of sub-chambers 402 and 403. Achuck 417 is positioned within the lower sub-chamber 403 near the bottominner surface. The chuck 417 is configured to receive and hold asemiconductor wafer 419 upon which the etching and deposition processesare performed. The chuck 417 can be an electrostatic chuck forsupporting the wafer 419 when present. In some embodiments, an edge ring(not shown) surrounds chuck 417, and has an upper surface that isapproximately planar with a top surface of the wafer 419, when presentover chuck 417. The chuck 417 also includes electrostatic electrodes forchucking and dechucking the wafer 419. A filter and DC clamp powersupply (not shown) may be provided for this purpose. Other controlsystems for lifting the wafer 419 off the chuck 417 can also beprovided. The chuck 417 can be electrically charged using an RF powersupply 423. The RF power supply 423 is connected to matching circuitry421 through a connection 427. The matching circuitry 421 is connected tothe chuck 417 through a connection 425. In this manner, the RF powersupply 423 is connected to the chuck 417. In various embodiments, a biaspower of the electrostatic chuck may be set at about 50 Vb or may be setat a different bias power depending on the process performed inaccordance with disclosed embodiments. For example, the bias power maybe between about 20 Vb and about 100 Vb, or between about 30 Vb andabout 150 Vb.

Elements for plasma generation include a coil 433 is positioned abovewindow 411. In some embodiments, a coil is not used in disclosedembodiments. The coil 433 is fabricated from an electrically conductivematerial and includes at least one complete turn. The example of a coil433 shown in FIG. 4 includes three turns. The cross-sections of coil 433are shown with symbols, and coils having an “X” extend rotationally intothe page, while coils having a “*” extend rotationally out of the page.Elements for plasma generation also include an RF power supply 441configured to supply RF power to the coil 433. In general, the RF powersupply 441 is connected to matching circuitry 439 through a connection445. The matching circuitry 439 is connected to the coil 433 through aconnection 443. In this manner, the RF power supply 441 is connected tothe coil 433. An optional Faraday shield 449 a is positioned between thecoil 433 and the window 411. The Faraday shield 449 a may be maintainedin a spaced apart relationship relative to the coil 433. In someembodiments, the Faraday shield 449 a is disposed immediately above thewindow 411. In some embodiments, the Faraday shield 449 b is between thewindow 411 and the chuck 417. In some embodiments, the Faraday shield449 b is not maintained in a spaced apart relationship relative to thecoil 433. For example, the Faraday shield 449 b may be directly belowthe window 411 without a gap. The coil 433, the Faraday shield 449 a,and the window 411 are each configured to be substantially parallel toone another. The Faraday shield 449 a may prevent metal or other speciesfrom depositing on the window 411 of the process chamber 424.

Process gas (e.g. H₂ and He, etc.) may be flowed into the processchamber through one or more main gas flow inlets 460 positioned in theupper sub-chamber 402 and/or through one or more side gas flow inlets470. Likewise, though not explicitly shown, similar gas flow inlets maybe used to supply process gases to a capacitively coupled plasmaprocessing chamber. A vacuum pump, e.g., a one or two stage mechanicaldry pump and/or turbomolecular pump 440, may be used to draw processgases out of the process chamber 424 and to maintain a pressure withinthe process chamber 424. For example, the vacuum pump may be used toevacuate the lower sub-chamber 403 during a purge operation of Avalve-controlled conduit may be used to fluidically connect the vacuumpump to the process chamber 424 so as to selectively control applicationof the vacuum environment provided by the vacuum pump. This may be doneemploying a closed-loop-controlled flow restriction device, such as athrottle valve (not shown) or a pendulum valve (not shown), duringoperational plasma processing. Likewise, a vacuum pump and valvecontrolled fluidic connection to the capacitively coupled plasmaprocessing chamber may also be employed.

During operation of the apparatus 400, one or more process gases such asan H₂-containing gas, may be supplied through the gas flow inlets 460and/or 470. In certain embodiments, process gas may be supplied onlythrough the main gas flow inlet 460, or only through the side gas flowinlet 470. In some cases, the gas flow inlets shown in the figure may bereplaced by more complex gas flow inlets, one or more showerheads, forexample. The Faraday shield 449 a and/or optional grid 450 may includeinternal channels and holes that allow delivery of process gases to theprocess chamber 424. Either or both of Faraday shield 449 a and optionalgrid 450 may serve as a showerhead for delivery of process gases. Insome embodiments, a liquid vaporization and delivery system may besituated upstream of the process chamber 424, such that once a liquidreactant or precursor is vaporized, the vaporized reactant or precursoris introduced into the process chamber 424 via a gas flow inlet 460and/or 470.

Radio frequency power is supplied from the RF power supply 441 to thecoil 433 to cause an RF current to flow through the coil 433. The RFcurrent flowing through the coil 433 generates an electromagnetic fieldabout the coil 433. The electromagnetic field generates an inductivecurrent within the upper sub-chamber 402. The physical and chemicalinteractions of various generated ions and radicals with the wafer 419etch features of and selectively deposit layers on the wafer 419.

If the plasma grid 450 is used such that there is both an uppersub-chamber 402 and a lower sub-chamber 403, the inductive current actson the gas present in the upper sub-chamber 402 to generate anelectron-ion plasma in the upper sub-chamber 402. The optional internalplasma grid 450 limits the amount of hot electrons in the lowersub-chamber 403. In some embodiments, the apparatus 400 is designed andoperated such that the plasma present in the lower sub-chamber 403 is anion-ion plasma.

Both the upper electron-ion plasma and the lower ion-ion plasma maycontain positive and negative ions, though the ion-ion plasma will havea greater ratio of negative ions to positive ions. Volatile etchingand/or deposition byproducts may be removed from the lower sub-chamber403 through port 422. For example, tin hydride generated during etchingof tin oxide using H₂ plasma can be removed through port 422 duringpurging and/or evacuation. The chuck 417 disclosed herein may operate atelevated temperatures ranging between about 10° C. and about 250° C. Thetemperature will depend on the process operation and specific recipe. Insome embodiments the apparatus is controlled to conduct the etching at atemperature of less than about 100° C.

Apparatus 400 may be coupled to facilities (not shown) when installed ina clean room or a fabrication facility. Facilities include plumbing thatprovide processing gases, vacuum, temperature control, and environmentalparticle control. These facilities are coupled to apparatus 400, wheninstalled in the target fabrication facility. Additionally, apparatus400 may be coupled to a transfer chamber that allows robotics totransfer semiconductor wafers into and out of apparatus 400 usingtypical automation.

In some embodiments, a system controller 430 (which may include one ormore physical or logical controllers) controls some or all of theoperations of a process chamber 424. The system controller 430 mayinclude one or more memory devices and one or more processors. In someembodiments, the apparatus 400 includes a switching system forcontrolling flow rates of the process gases. The controller, in someembodiments, includes program instructions for causing the steps of anyof the methods provided herein.

In some implementations, the system controller 430 is part of a system,which may be part of the above-described examples. Such systems caninclude semiconductor processing equipment, including a processing toolor tools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be integrated intothe system controller 430, which may control various components orsubparts of the system or systems. The system controller, depending onthe processing parameters and/or the type of system, may be programmedto control any of the processes disclosed herein, including the deliveryof processing gases, temperature settings (e.g., heating and/orcooling), pressure settings, vacuum settings, power settings, radiofrequency (RF) generator settings, RF matching circuit settings,frequency settings, flow rate settings, fluid delivery settings,positional and operation settings, wafer transfers into and out of atool and other transfer tools and/or load locks connected to orinterfaced with a specific system.

Broadly speaking, the system controller 430 may be defined aselectronics having various integrated circuits, logic, memory, and/orsoftware that receive instructions, issue instructions, controloperation, enable cleaning operations, enable endpoint measurements, andthe like. The integrated circuits may include chips in the form offirmware that store program instructions, digital signal processors(DSPs), chips defined as application specific integrated circuits(ASICs), and/or one or more microprocessors, or microcontrollers thatexecute program instructions (e.g., software). Program instructions maybe instructions communicated to the controller in the form of variousindividual settings (or program files), defining operational parametersfor carrying out a particular process on or for a semiconductor wafer orto a system. The operational parameters may, in some embodiments, bepart of a recipe defined by process engineers to accomplish one or moreprocessing steps during the fabrication or removal of one or morelayers, materials, metals, oxides, silicon, silicon dioxide, surfaces,circuits, and/or dies of a wafer.

The system controller 430, in some implementations, may be a part of orcoupled to a computer that is integrated with, coupled to the system,otherwise networked to the system, or a combination thereof. Forexample, the controller may be in the “cloud” or all or a part of a fabhost computer system, which can allow for remote access of the waferprocessing. The computer may enable remote access to the system tomonitor current progress of fabrication operations, examine a history ofpast fabrication operations, examine trends or performance metrics froma plurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the system controller 430 receivesinstructions in the form of data, which specify parameters for each ofthe processing steps to be performed during one or more operations. Itshould be understood that the parameters may be specific to the type ofprocess to be performed and the type of tool that the controller isconfigured to interface with or control. Thus as described above, thesystem controller 430 may be distributed, such as by including one ormore discrete controllers that are networked together and workingtowards a common purpose, such as the processes and controls describedherein. An example of a distributed controller for such purposes wouldbe one or more integrated circuits on a chamber in communication withone or more integrated circuits located remotely (such as at theplatform level or as part of a remote computer) that combine to controla process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, an ALDchamber or module, an ALE chamber or module, an ion implantation chamberor module, a track chamber or module, and any other semiconductorprocessing systems that may be associated or used in the fabricationand/or manufacturing of semiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller might communicate with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

FIG. 12 depicts a semiconductor process cluster architecture withvarious modules that interface with a vacuum transfer module 538 (VTM).The arrangement of various modules to “transfer” wafers among multiplestorage facilities and processing modules may be referred to as a“cluster tool architecture” system. Airlock 530, also known as aloadlock or transfer module, interfaces with the VTM 538 which, in turn,interfaces with four processing modules 520 a-520 d, which may beindividual optimized to perform various fabrication processes. By way ofexample, processing modules 520 a-520 d may be implemented to performsubstrate etching, deposition, ion implantation, wafer cleaning,sputtering, and/or other semiconductor processes. In some embodiments,tin oxide deposition and tin oxide etching are performed in the samemodule. In some embodiments, tin oxide deposition and tin oxide etchingare performed in different modules of the same tool. One or more of thesubstrate etching processing modules (any of 520 a-520 d) may beimplemented as disclosed herein, e.g., for depositing conformal films,selectively etching tin oxide, forming air gaps, and other suitablefunctions in accordance with the disclosed embodiments. Airlock 530 andprocessing modules 520 a-520 d may be referred to as “stations.” Eachstation has a facet 536 that interfaces the station to VTM 538. Insideeach facet, sensors 1-18 are used to detect the passing of wafer 526when moved between respective stations.

Robot 522 transfers wafer 526 between stations. In one embodiment, robot522 has one arm, and in another embodiment, robot 522 has two arms,where each arm has an end effector 524 to pick wafers such as wafer 526for transport. Front-end robot 532, in atmospheric transfer module (ATM)540, is used to transfer wafers 526 from cassette or Front OpeningUnified Pod (FOUP) 534 in Load Port Module (LPM) 542 to airlock 530.Module center 528 inside processing modules 520 a-520 d is one locationfor placing wafer 526. Aligner 544 in ATM 540 is used to align wafers.

In an exemplary processing method, a wafer is placed in one of the FOUPs534 in the LPM 542. Front-end robot 532 transfers the wafer from theFOUP 534 to an aligner 544, which allows the wafer 526 to be properlycentered before it is etched or processed. After being aligned, thewafer 526 is moved by the front-end robot 532 into an airlock 530.Because the airlock 530 has the ability to match the environment betweenan ATM 540 and a VTM 538, the wafer 526 is able to move between the twopressure environments without being damaged. From the airlock 530, thewafer 526 is moved by robot 522 through VTM 538 and into one of theprocessing modules 520 a-520 d. In order to achieve this wafer movement,the robot 522 uses end effectors 524 on each of its arms. Once the wafer526 has been processed, it is moved by robot 522 from the processingmodules 520 a-520 d to the airlock 530. From here, the wafer 526 may bemoved by the front-end robot 532 to one of the FOUPs 534 or to thealigner 544.

It should be noted that the computer controlling the wafer movement canbe local to the cluster architecture, or can be located external to thecluster architecture in the manufacturing floor, or in a remote locationand connected to the cluster architecture via a network. A controller asdescribed above with respect to FIG. 11 may be implemented with the toolin FIG. 12 . Machine-readable media containing instructions forcontrolling process operations in accordance with the present inventionmay be coupled to the system controller.

In some embodiments an apparatus is provided, where the apparatusincludes a process chamber having a substrate holder configured forholding the semiconductor substrate during etching; a plasma generatorconfigured for generating a plasma in a process gas; and a controller.The controller includes program instructions for implementing any of themethods describing herein.

In another aspect a non-transitory computer machine-readable medium isprovided, where it includes code for causing the performance of any ofthe methods described herein.

In another aspect, a system for forming spacers or hardmasks on asemiconductor substrate is provided. The system includes one or moredeposition chambers; one or more etch chambers; and a controller. Thecontroller includes program instructions for implementing any methodsdescribed herein. In another aspect, the system includes any of theapparatuses and systems described herein and a stepper. In anotheraspect, a system for processing a semiconductor substrate is provided.In one embodiment the system includes: one or more deposition chambers;one or more etch chambers; and a system controller comprising programinstructions for: (i) causing a deposition of a tin oxide layer overhorizontal surfaces and sidewalls of a plurality of protruding featureson the semiconductor substrate; (ii) causing a formation of apassivation layer on the tin oxide layer at the sidewalls of theprotruding features, and (iii) causing a removal of the tin oxide layerfrom horizontal surfaces of the protruding features, without causing aremoval of the tin oxide layer over the sidewalls of the protrudingfeatures.

Alternating Etch and Passivation Process

In some embodiments the etching of tin oxide in various semiconductorprocessing methods described herein is performed in a presence ofexposed silicon-containing layers, such as amorphous silicon, SiOC,SiON, SiONC, SiN, SiC, and SiO₂. In some embodiments thesilicon-containing layer is further protected from undesired etchingthat may occur during the tin oxide etch.

An example of a process flow diagram that utilizes such protection isshown in FIG. 13 . The process starts in 1301 by providing a substratehaving a silicon-containing layer, where the substrate further includesan exposed tin oxide layer (e.g., a tin oxide footing on a silicon oxidelayer). An example of such substrate is shown in FIG. 14A, which isidentical to FIG. 3C. In FIG. 14A, the substrate includes a protrudingfeature 305 disposed on an etch stop layer 303. The etch stop layer inthe illustrated embodiment is a silicon-containing layer, such asamorphous silicon, SiOC, SiON, SiONC, SiN, SiC, or SiO₂. The tin oxidelayer 307 resides at the sidewalls of the protruding feature 305 andforms a footing (a lateral expansion at the bottom of the protrudingfeature), which needs to be reduced in order to form tin oxide spacerswith consistent distance. While in some embodiments the footing can beefficiently removed as described with reference to FIG. 3D, in somecases etching of the footing can cause inadvertent etching of the etchstop layer 303. This inadvertent etching can occur, in one example if achlorine-based etch chemistry (e.g., Cl₂/BCl₃ etch) is used during etchof tin oxide, and where the silicon-containing layer is SiOC.

Referring to FIG. 13 , in operation 1303, the silicon-containing layeris passivated. The passivation is a treatment that makes thesilicon-containing layer more resistant to a tin oxide etch chemistry.In one example, passivation is performed by treating a substrate with anoxygen-containing reactant, such as by treating the substrate with anoxygen-containing reactant in a plasma. For example, plasma may beformed in a process gas that includes O₂, O₃, SO₂, CO₂, or anycombination of these oxygen-containing reactants. In some embodimentsthe treatment results in formation of silicon-oxygen bonds at the outerexposed portion of the silicon-containing layer. For example, a SiOClayer may be made more oxygen-rich after the passivation treatment. Inanother example, a silicon oxide etch stop layer deposited by CVD,contains residual carbon and hydrogen, and passivation with anoxygen-containing reactant can reduce the content of carbon and hydrogenin the layer, and make it more resistant towards tin oxide etchchemistry. The substrate having a passivated etch stop layer 304 isshown in FIG. 14B. In another embodiment the passivation is performed bytreating the substrate with a nitrogen containing reactant, such as witha nitrogen-containing reactant (e.g., N₂) in a plasma. The purpose ofthe passivation treatment is to make the silicon-containing material(e.g., etch stop layer material) more resistant to a tin oxide chemistrythat is used for tin oxide etching, such as a chlorine-based etchchemistry, or a hydrogen-based etch chemistry.

In operation 1305, tin oxide is etched. Tin oxide can be etched usingany of the methods described herein, such as by exposing the substrateto a chlorine-based chemistry (e.g., Cl₂ and/or BCl₃ in a plasma),and/or a hydrogen-based chemistry (e.g., treatment with H₂, HBr, ahydrocarbon or a combination thereof, as described herein). The reactantgases (e.g., Cl₂ and/or BCl₃) may be provided together with an inertdiluent gas, such as helium, argon, neon, or xenon. In operation 1307,the passivation step 1303 and the etching step 1305 are repeated in analternating fashion. It is noted that the first passivation step may beperformed before or after the first etching step. For example, themethod may have an etch/passivation/etch/passivation sequence, or apassivation/etch/passivation/etch sequence. In some embodiments themethod involves between 2-50, such as between 5-20 etch and passivationsteps (i.e. each of etch and passivation steps is performed between2-50, such as between 5-20 steps). The structure obtained after therequired number of etching and passivation is illustrated in FIG. 14C.In one specific example each etching step is performed for about 10seconds and each passivation step is performed for 5 seconds, where themethod involves performing between 8-20 of each of the steps in analternating fashion.

The alternating etching and passivation sequence described herein canprovide several advantages. First, undesired etching of thesilicon-containing etch stop layer can be minimized, while sidewallthickness can be retained. Further, the footing can be efficientlyremoved. It is noted that the method described herein can be used forprotecting any silicon-containing layer during etching of exposed tinoxide, but is particularly useful for removing tin oxide footing asdescribed with reference to FIGS. 14A-14C. It is noted that siliconoxide is generally more resistant to etching than othersilicon-containing materials, and provided methods are particularlyuseful for protecting such materials as SiOC, amorphous silicon, SiOCN,and SiC, although these methods can also be used for passivation ofsilicon oxide. In one specific implementation the substrate containingsuch materials is passivated using an oxygen-containing reactant (e.g.,O₂, O₃, SO₂, or CO₂ in a plasma), which makes the silicon-containingmaterial more resistant to a chlorine-based tin oxide etch chemistry(e.g., Cl₂/BCl₃ chemistry) and hydrogen-based tin oxide etch chemistry(e.g., H₂, HBr, hydrocarbon etch). Therefore, in some embodiments theprocess involves alternating passivation with an oxygen-containingreactant and tin oxide etching using a chlorine-based chemistry and/or ahydrogen-based chemistry as described herein.

In one example it was possible to decrease tin oxide sidewall loss from5 nm to less than 1 nm when provided method was implemented and todecrease bottom SiOC layer loss from 5 nm to 1 nm. The tin oxide footingwas decreased from 6 nm to 1 nm by implementing these methods. It isnoted that provided methods can be implemented with or without use oftin oxide passivation layer 309.

In one example, a substrate containing an exposed amorphous silicon etchstop layer and an exposed tin oxide layer (during formation of tin oxidespacer) was passivated to make the amorphous silicon etch stop layermore resistant to tin oxide etch chemistry. Passivation was conducted at40 degrees C., and 5 mTorr by exposing the substrate to a plasma formedin a process gas that consisted of O₂ (provided at 200 sccm). The plasmawas formed using 13.56 MHz RF frequency and 400 W power per one 300 mmsubstrate. After passivation, the process chamber was purged with argon,and tin oxide was etched at 40 degrees C., and 10 mTorr by exposing thesubstrate to a plasma formed in a process gas that consisted of 10 sccmBCl₃ (provided at 10 sccm), 190 sccm Cl₂ (provided at 190 sccm) andhelium (provided at 200 sccm). The plasma was formed using 13.56 MHz RFfrequency and 400 W power per one 300 mm substrate. The process chamberwas then purged and the passivation and etch steps (each followed bypurging) were repeated in an alternating fashion until the spacerfooting of tin oxide was removed.

In another aspect, an apparatus is provided (e.g., any of the etchingtools described herein), where the apparatus includes: (a) a processingchamber having a support for the semiconductor substrate and an inletfor introduction of one or more reactants into the processing chamber;and (b) a controller comprising program instructions for: (i) causingpassivation a silicon-containing layer on a semiconductor substratetowards a tin oxide etch chemistry; (ii) causing etching of a tin oxideon a semiconductor substrate; and (iii) causing a repeating, in analternating fashion of (i) and (ii). The controller may be furtherprogrammed to perform any of the methods described herein.

FURTHER IMPLEMENTATIONS

The apparatus and processes described herein may be used in conjunctionwith lithographic patterning tools or processes, for example, for thefabrication or manufacture of semiconductor devices, displays, LEDs,photovoltaic panels, and the like. Typically, though not necessarily,such apparatus and processes will be used or conducted together in acommon fabrication facility. Lithographic patterning of a film typicallycomprises some or all of the following steps, each step enabled with anumber of possible tools: (1) application of photoresist on a workpiece, i.e., a substrate, using a spin-on or spray-on tool; (2) curingof photoresist using a hot plate or furnace or UV curing tool; (3)exposing the photoresist to visible or UV or x-ray light with a toolsuch as a wafer stepper; (4) developing the resist so as to selectivelyremove resist and thereby pattern it using a tool such as a wet bench;(5) transferring the resist pattern into an underlying film or workpiece by using a dry or plasma-assisted etching tool; and (6) removingthe resist using a tool such as an RF or microwave plasma resiststripper.

What is claimed is:
 1. A method of processing a semiconductor substrate,the method comprising: (a) providing a semiconductor substrate having anexposed silicon-containing material and an exposed tin oxide; (b)passivating the exposed silicon-containing material towards a tin oxideetch chemistry; (c) etching the exposed tin oxide using the tin oxideetch chemistry; and (d) repeating operations (b) and (c) such thatoperations (b) and (c) are performed in an alternating fashion.
 2. Themethod of claim 1, wherein the exposed silicon-containing material isselected from the group consisting of amorphous silicon, silicon oxide,SiON, SiOC, SiONC, SiC, and SiN.
 3. The method of claim 1, wherein (c)comprises etching tin oxide using a chlorine-based etch chemistry thatcomprises exposing the semiconductor substrate to a plasma-activatedchlorine-containing reactant selected from the group consisting of Cl₂,BCl₃, and combinations thereof.
 4. The method of claim 1, wherein (c)comprises etching the tin oxide using a hydrogen-based etch chemistrythat results in a formation of a tin hydride.
 5. The method of claim 1,wherein (c) comprises etching the tin oxide using a hydrogen-based etchchemistry, by contacting the semiconductor substrate with aplasma-activated hydrogen-containing reactant selected from the groupconsisting of H₂, HBr, NH₃, H₂O, a hydrocarbon, and combinationsthereof.
 6. The method of claim 1, wherein (c) comprises etching tinoxide using a chlorine-based etch chemistry that comprises exposing thesemiconductor substrate to a plasma-activated process gas comprising achlorine-containing reactant selected from the group consisting of Cl₂,BCl₃, and combinations thereof, and a diluent gas selected from thegroup consisting from helium, neon, argon, and xenon and combinationsthereof.
 7. The method of claim 1, wherein (b) comprises treating thesubstrate with an oxygen-containing reactant.
 8. The method of claim 1,wherein (b) comprises treating the substrate with a plasma-activatedoxygen-containing reactant.
 9. The method of claim 1, wherein (b)comprises treating the substrate with a plasma formed in a process gascomprising a gas selected from the group consisting of O₂, O₃, SO₂, andCO₂.
 10. The method of claim 1, wherein (b) is performed before (c). 11.The method of claim 1, wherein (c) is performed before (b).
 12. Themethod of claim 1, wherein operations (b) and (c) are performed between2-50 times.
 13. The method of claim 1, wherein the silicon-containingmaterial is selected from the group consisting of amorphous silicon,silicon oxide, SiON, SiOC, SiONC, SiC, and SiN, wherein the passivatingin (b) comprises treating the substrate with a plasma-activatedoxygen-containing reactant, and wherein (c) comprises etching the tinoxide using a chlorine-based etch chemistry that comprises exposing thesemiconductor substrate to a plasma-activated chlorine-containingreactant selected from the group consisting of Cl₂, BCl₃, andcombinations thereof.
 14. The method of claim 1, wherein (b) comprisestreating the semiconductor substrate with a nitrogen-containingreactant.